# Chapter 4: Newton's Second Law Of Motion, Force And Acceleration

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• 1.

### Which has the greater mass?

• A.

A king-size pillow

• B.

An automobile battery

• C.

) neither â€“ both have the same

B. An automobile battery
Explanation
An automobile battery has a greater mass compared to a king-size pillow. This is because automobile batteries are generally made of heavy materials such as lead and have a larger size and weight compared to a pillow, which is typically filled with lightweight materials like feathers or synthetic fibers. Therefore, the battery would have a greater mass.

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• 2.

### A kilogram is a measure of an object's

• A.

Weight

• B.

Force

• C.

Mass

• D.

Size

C. Mass
Explanation
A kilogram is a measure of an object's mass. Mass refers to the amount of matter in an object, and it remains the same regardless of the object's location or the force acting on it. Weight, on the other hand, is the force exerted on an object due to gravity and can vary depending on the object's location. Size is a measure of an object's dimensions and is unrelated to mass. Therefore, the correct answer is mass.

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• 3.

### Compared to a 1-kg block of solid iron, a 2-kg block of solid iron has twice as much

• A.

Inertia

• B.

Mass

• C.

Volume

• D.

All of these

• E.

None of these

D. All of these
Explanation
A 2-kg block of solid iron compared to a 1-kg block of solid iron has twice as much inertia, mass, and volume. Inertia is the resistance of an object to changes in its motion, and since the 2-kg block has more mass, it will have more inertia. Mass is the amount of matter in an object, so the 2-kg block will indeed have twice as much mass as the 1-kg block. Volume refers to the amount of space occupied by an object, and since the 2-kg block is larger, it will have a greater volume. Therefore, all of these statements are true.

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• 4.

### Compared to a 1-kg block of solid iron, a 2-kg block of solid iron has the same

• A.

Mass

• B.

Volume

• C.

Weight

• D.

All of these

• E.

None of these

E. None of these
Explanation
The statement "none of these" implies that a 2-kg block of solid iron does not have the same mass, volume, or weight as a 1-kg block of solid iron. This is because mass, volume, and weight are all dependent on the amount of matter present, and in this case, the amount of matter is different (1 kg vs. 2 kg). Therefore, none of these properties are the same for both blocks.

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• 5.

• A.

• B.

The gravitational attraction force between you and the Earth

• C.

A property of mechanical equilibrium

• D.

All of these

B. The gravitational attraction force between you and the Earth
Explanation
The correct answer is "the gravitational attraction force between you and the Earth." Weight is the force exerted on an object due to gravity, and it is directly proportional to an object's mass. Therefore, your weight is equal to the gravitational attraction force between you and the Earth.

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• 6.

### If one object has twice as much mass as another object, it also has twice as much

• A.

Inertia

• B.

Velocity

• C.

Acceleration due to gravity

• D.

Volume

• E.

All of these

A. Inertia
Explanation
The correct answer is inertia. Inertia is the property of an object to resist changes in its motion. It depends on the mass of the object, so if one object has twice as much mass as another object, it will also have twice as much inertia. Velocity, acceleration due to gravity, and volume are not directly related to the mass of an object.

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• 7.

### Compared to the mass of a certain object on Earth, the mass of the same object on the moon is

• A.

One sixth as much

• B.

The same

• C.

Six times as much

• D.

Zero

B. The same
Explanation
The mass of an object remains the same regardless of its location. Therefore, the mass of a certain object on the moon would be the same as its mass on Earth.

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• 8.

### Strange as it may seem, it is just as hard to accelerate a car on a level surface on the moon as it is here on the Earth. This is because

• A.

The mass of the car is independent of gravity

• B.

The weight of the car is independent of gravity

• C.

Nonsense! A car is much more easily accelerated on the moon than on the Earth

A. The mass of the car is independent of gravity
Explanation
The correct answer is that the mass of the car is independent of gravity. This means that the amount of matter in the car, which determines its inertia and resistance to acceleration, remains the same regardless of the gravitational force acting on it. Therefore, the car would require the same amount of force to accelerate on the moon as it would on Earth, despite the difference in gravity.

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• 9.

### A ride on a roller-coaster car containing 6 passengers takes 3 minutes. Neglecting friction, a similar ride with 12 passengers aboard would take

• A.

1.5 minutes

• B.

3 minutes

• C.

6 minutes

• D.

18 minutes

B. 3 minutes
Explanation
The time it takes for a roller-coaster ride with a certain number of passengers is not affected by the number of passengers. Therefore, a similar ride with 12 passengers would still take 3 minutes, as stated in the answer.

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• 10.

### The newton is a unit of

• A.

Force

• B.

Mass

• C.

Density

• D.

Inertia

A. Force
Explanation
The newton is a unit of force. Force is a physical quantity that can cause an object to accelerate or deform. It is measured in newtons, and it is the product of mass and acceleration. In other words, force is the push or pull that one object exerts on another object. The newton is named after Sir Isaac Newton, a renowned physicist and mathematician who made significant contributions to the study of motion and force.

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• 11.

### In which case would you have the largest mass of gold? If your chunk of gold weighed 1 N on the

• A.

Moon

• B.

Earth

• C.

Planet Jupiter

A. Moon
Explanation
The mass of an object remains the same regardless of its location, as mass is a measure of the amount of matter in an object. However, weight is the force exerted on an object due to gravity, and it depends on the gravitational pull of the celestial body. Since the gravitational pull on the moon is weaker compared to Earth or Jupiter, the chunk of gold would weigh less on the moon. Therefore, to have the largest mass of gold, one would need to be on the moon.

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• 12.

### A rock weighs 30 N on Earth. A second rock weighs 30 N on the moon. Which of the two rocks has the greater mass?

• A.

The one on Earth

• B.

The one on the moon

• C.

They have the same mass

• D.

Not enough information to say

B. The one on the moon
Explanation
The weight of an object depends on the gravitational force acting on it, which is determined by the mass of the object and the strength of the gravitational field. Since both rocks have the same weight of 30 N, it means that the gravitational force acting on them is the same. However, the strength of the gravitational field on the moon is about 1/6th of that on Earth. Therefore, for the rock on the moon to have the same weight as the rock on Earth, it must have a smaller mass. Hence, the rock on the moon has a smaller mass than the one on Earth.

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• 13.

### An object's weight may properly be expressed in units of

• A.

Meters

• B.

Kilograms

• C.

Newtons

• D.

Cubic centimeters

C. Newtons
Explanation
An object's weight is a measure of the force exerted on it due to gravity. The unit of measurement for force is newtons. Therefore, it is appropriate to express an object's weight in newtons. Meters, kilograms, and cubic centimeters are units of length, mass, and volume respectively, and are not suitable for measuring weight.

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• 14.

### A force is a vector quantity because it has both

• A.

Magnitude and direction

• B.

Mass and acceleration

• C.

Action and reaction counterparts

A. Magnitude and direction
Explanation
A force is considered a vector quantity because it has both magnitude and direction. Magnitude refers to the size or strength of the force, while direction indicates the path or orientation in which the force is applied. These two components are essential in fully describing a force and understanding its effects on an object or system.

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• 15.

### A 10-kg brick and a 1-kg book are dropped in a vacuum. The force of gravity on the 10-kg brick is

• A.

The same as the force on the 1-kg book

• B.

10 times as much

• C.

One-tenth as much

• D.

Zero

B. 10 times as much
Explanation
In a vacuum, both the 10-kg brick and the 1-kg book experience the same force of gravity. The force of gravity is directly proportional to the mass of an object. Since the brick has a mass that is 10 times greater than the book, it will experience a force of gravity that is 10 times as much as the force experienced by the book. Therefore, the correct answer is that the force of gravity on the 10-kg brick is 10 times as much as the force on the 1-kg book.

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• 16.

### An object is propelled along a straight-line path by a force. If the net force were doubled, the object's acceleration would be

• A.

Half as much

• B.

The same

• C.

Twice as much

• D.

Four times as much

• E.

None of these

C. Twice as much
Explanation
If the net force acting on an object is doubled, according to Newton's second law of motion (F = ma), the acceleration of the object would also double. This is because acceleration is directly proportional to the force applied on an object. Therefore, if the force is doubled, the acceleration will also be doubled.

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• 17.

### If an object's mass is decreasing while a constant force is applied to the object, the acceleration

• A.

Decreases

• B.

Increases

• C.

Remains the same

B. Increases
Explanation
When an object's mass is decreasing while a constant force is applied, the acceleration of the object increases. This is because the force is constant, but the mass is decreasing. According to Newton's second law of motion (F = ma), when the mass decreases, the acceleration must increase to maintain the same force. So, as the object becomes lighter, it experiences a greater acceleration.

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• 18.

### An object is propelled along a straight-line path in space by a force. If the mass of the object somehow becomes twice as much, its acceleration

• A.

• B.

Doubles

• C.

Stays the same

• D.

Halves

• E.

None of these

D. Halves
Explanation
When the mass of an object becomes twice as much, its acceleration halves. This is because acceleration is inversely proportional to mass according to Newton's second law of motion (F = ma). If the mass doubles, the force required to accelerate the object remains the same, but since the mass has increased, the acceleration decreases by half to maintain the equilibrium.

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• 19.

### An object is pulled northward by a force of 10 N and at the same time another force of 15 N pulls it southward. The magnitude of the resultant force on the object is

• A.

0 N

• B.

5 N

• C.

25 N

• D.

150 N

B. 5 N
Explanation
The magnitude of the resultant force on the object is 5 N because the forces pulling in opposite directions will cancel each other out partially. The northward force of 10 N will be partially counteracted by the southward force of 15 N, resulting in a net force of 5 N in the northward direction.

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• 20.

### The force of friction on a sliding object is 10 newtons. The applied force needed to maintain a constant velocity is

• A.

More than 10 N

• B.

Less than 10 N

• C.

10 N

C. 10 N
Explanation
The applied force needed to maintain a constant velocity is equal to the force of friction. In this case, the force of friction is 10 newtons, so the applied force needed to maintain a constant velocity is also 10 newtons.

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• 21.

### A 10-N falling object encounters 4 N of air resistance. The net force on the object is

• A.

0 N

• B.

4 N

• C.

6 N

• D.

10 N

• E.

None of these

C. 6 N
Explanation
The net force on the object is 6 N because it is the difference between the force of gravity (10 N) and the force of air resistance (4 N). The net force is the overall force acting on the object, taking into account both the forces acting in the same direction and those acting in opposite directions. In this case, the force of gravity is acting downwards, while the force of air resistance is acting upwards. Therefore, the net force is the difference between these two forces, resulting in a net force of 6 N acting downwards on the object.

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• 22.

### A 10-N falling object encounters 10 N of air resistance. The net force on the object is

• A.

0 N

• B.

4 N

• C.

6 N

• D.

10 N

• E.

None of these

A. 0 N
Explanation
When an object is falling, it experiences two forces: gravity pulling it downward and air resistance pushing it upward. In this case, the object encounters 10 N of air resistance, which cancels out the 10 N force of gravity. Therefore, the net force on the object is 0 N.

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• 23.

### An apple weighs 1 N. When held at rest above your head, the net force on the apple is

• A.

0 N

• B.

0.1 N

• C.

1 N

• D.

9.8 N

• E.

None of these

A. 0 N
Explanation
When an apple is held at rest above your head, the net force on the apple is 0 N. This is because the apple is not moving, so there is no acceleration and therefore no net force acting on it. The force of gravity pulling the apple downwards is balanced by the force exerted by your hand holding it up, resulting in a net force of 0 N.

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• 24.

### An apple at rest weighs 1 N. The net force on the apple when it is in free fall is

• A.

0 N

• B.

0.1 N

• C.

1 N

• D.

9.8 N

• E.

None of these

C. 1 N
Explanation
When an object is in free fall, it experiences a gravitational force acting on it. In this case, the apple weighs 1 N when at rest, which means that the gravitational force acting on it is also 1 N. Therefore, the net force on the apple when it is in free fall is 1 N.

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• 25.

### Which has zero acceleration? An object

• A.

At rest

• B.

Moving at constant velocity

• C.

In mechanical equilibrium

• D.

All of these

• E.

None of these

D. All of these
Explanation
All of these options have zero acceleration. An object at rest has zero velocity and therefore zero acceleration. An object moving at constant velocity also has zero acceleration because its velocity is not changing. An object in mechanical equilibrium has zero net force acting on it, which means it has zero acceleration. Therefore, all of these options have zero acceleration.

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• 26.

### Whenever the net force on an object is zero, its acceleration

• A.

May be less than zero

• B.

Is zero

• C.

May be more than zero

B. Is zero
Explanation
When the net force on an object is zero, it means that all the forces acting on the object are balanced and cancel each other out. In this case, the object's acceleration will be zero. This is because acceleration is directly proportional to the net force acting on an object according to Newton's second law of motion. If the net force is zero, there is no unbalanced force to cause acceleration, resulting in a zero acceleration.

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• 27.

### The maximum acceleration of a car while towing a second car twice its mass, compared to its acceleration with no car in tow, is

• A.

One half

• B.

One third

• C.

One fourth

• D.

The same

• E.

None of these

B. One third
Explanation
When a car is towing a second car that is twice its mass, the force required to accelerate both cars is greater than the force required to accelerate just the first car. According to Newton's second law of motion (F = ma), the acceleration of an object is directly proportional to the force applied to it and inversely proportional to its mass. Therefore, the car's acceleration while towing the second car will be one-third of its acceleration with no car in tow, as the force required to accelerate both cars is three times greater (twice the mass of the second car plus the mass of the first car).

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• 28.

### Your car is coasting on level ground at 60 km/h and you apply the brakes until the car slows to 40 km/h. If you suddenly release the brakes now, the car tends to

• A.

Momentarily regain its higher initial speed

• B.

Continue moving at 40 km/h

• C.

Decrease in speed if no other forces act

B. Continue moving at 40 km/h
Explanation
When the brakes are released, the car tends to continue moving at the same speed it was at before, which in this case is 40 km/h. This is because there are no other forces acting on the car to slow it down or speed it up. The car will maintain its velocity unless acted upon by an external force, such as friction or gravity. Therefore, the correct answer is "continue moving at 40 km/h."

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• 29.

### A heavy block at rest is suspended by a vertical rope. When the block is accelerated upward by the rope, the rope tension

• A.

Increases

• B.

Decreases

• C.

Remains the same

A. Increases
Explanation
When the heavy block is accelerated upward by the rope, the rope tension increases. This is because the block's weight creates a downward force, and in order to accelerate the block upward, the rope needs to exert a greater upward force to counteract the weight. As a result, the tension in the rope increases to provide the necessary force to lift the block.

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• 30.

### A 1-kg mass at the Earth's surface weighs

• A.

1 N

• B.

4.9 N

• C.

9.8 N

• D.

10.8 N

• E.

None of these

C. 9.8 N
Explanation
The weight of an object is the force exerted on it due to gravity. On Earth's surface, the acceleration due to gravity is approximately 9.8 m/s^2. Using the formula weight = mass x acceleration due to gravity, we can calculate the weight of a 1-kg mass to be 9.8 N.

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• 31.

### If a non-rotating object has no acceleration, then we can say for certain that it is

• A.

At rest

• B.

Moving at constant non-zero velocity

• C.

In mechanical equilibrium

• D.

All of these

• E.

None of these

C. In mechanical equilibrium
Explanation
If a non-rotating object has no acceleration, it means that the net force acting on it is zero. In mechanical equilibrium, the sum of all forces acting on an object is zero, which means there is no acceleration. Therefore, if a non-rotating object has no acceleration, it can be concluded that it is in mechanical equilibrium.

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• 32.

### When you relax at rest with your left foot on one bathroom scale and your right foot on a similar scale, each of the scales will

• A.

• B.

Indicate part of your total weight but not necessarily half of it

• C.

• D.

Any of the above may be correct

D. Any of the above may be correct
Explanation
When you relax at rest with your left foot on one bathroom scale and your right foot on a similar scale, each of the scales may indicate exactly half your weight if your weight is evenly distributed between both feet. However, if your weight is not evenly distributed, the scales may indicate part of your total weight but not necessarily half of it. Additionally, if there is any imbalance or inconsistency in the scales, they may indicate different values that will equal your weight when added together. Therefore, any of the above options may be correct depending on the specific circumstances.

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• 33.

### Hang from a pair of gym rings and the upward support forces of the rings will always

• A.

• B.

Each be equal to your weight

• C.

Explanation
When hanging from a pair of gym rings, the upward support forces exerted by the rings will add up to equal your weight. This is because the rings provide an equal and opposite force to counteract your weight and keep you suspended. The combined upward forces from both rings are necessary to balance your downward force of gravity, resulting in equilibrium. Therefore, the total upward support forces of the rings will add up to equal your weight.

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• 34.

### A car has a mass of 1000 kg and accelerates at 2 meters per second per second. What is the magnitude of the net force exerted on the car?

• A.

500 N

• B.

1000 N

• C.

1500 N

• D.

2000 N

• E.

None of these

D. 2000 N
Explanation
The magnitude of the net force exerted on an object can be calculated using Newton's second law of motion, which states that force is equal to mass multiplied by acceleration. In this case, the mass of the car is given as 1000 kg and the acceleration is given as 2 meters per second per second. Therefore, the net force exerted on the car is equal to 1000 kg multiplied by 2 meters per second per second, which equals 2000 N.

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• 35.

### A tow truck exerts a force of 3000 N on a car, accelerating it at 2 meters per second per second. What is the mass of the car?

• A.

500 kg

• B.

1000 kg

• C.

1500 kg

• D.

3000 kg

• E.

None of these

C. 1500 kg
Explanation
The mass of an object can be determined using the formula F = ma, where F is the force exerted on the object and a is the acceleration. In this case, the force exerted by the tow truck is 3000 N and the acceleration of the car is 2 m/s^2. Plugging these values into the formula, we get 3000 N = m * 2 m/s^2. Solving for m, we find that the mass of the car is 1500 kg.

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• 36.

### A girl pulls on a 10-kg wagon with a constant horizontal force of 30 N. If there are no other horizontal forces, what is the wagon's acceleration in meters per second per second?

• A.

0.3

• B.

3.0

• C.

10

• D.

30

• E.

300

B. 3.0
Explanation
The wagon's acceleration can be calculated using Newton's second law, which states that the force applied to an object is equal to the mass of the object multiplied by its acceleration. In this case, the force applied to the wagon is 30 N and the mass of the wagon is 10 kg. Therefore, the acceleration of the wagon is 30 N / 10 kg = 3.0 m/s^2.

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• 37.

### If the mass of an object does not change, a constant net force on the object produces constant

• A.

Velocity

• B.

Acceleration

• C.

Both of these

• D.

Neither of these

B. Acceleration
Explanation
When the mass of an object does not change, a constant net force on the object will produce a constant acceleration. This is explained by Newton's second law of motion, which states that the acceleration of an object is directly proportional to the net force applied to it and inversely proportional to its mass. Since the mass is constant, a constant net force will result in a constant acceleration. Velocity, on the other hand, is the rate at which an object's position changes, and it is not directly affected by a constant net force. Therefore, the correct answer is acceleration.

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• 38.

### A force of 1 N accelerates a mass of 1 kg at the rate of 1 m/s2. The acceleration of a mass of 2 kg acted upon by a net force of 2 N is

• A.

Half as much

• B.

Twice as much

• C.

The same

• D.

None of these

C. The same
Explanation
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. In this case, the force and mass of the first object are both 1, resulting in an acceleration of 1 m/s^2. For the second object, the force is 2 and the mass is 2, which gives the same acceleration of 1 m/s^2. Therefore, the answer is that the acceleration of the second mass is the same as the first mass.

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• 39.

### A bag of groceries has a mass of 10 kilograms and a weight of

• A.

• B.

• C.

• D.

• E.

More than 1000 N

Explanation
The weight of an object is the force exerted on it due to gravity. The weight is directly proportional to the mass of the object. In this case, the bag of groceries has a mass of 10 kilograms, so its weight can be calculated using the formula weight = mass x acceleration due to gravity. The acceleration due to gravity is approximately 9.8 m/s^2. So, weight = 10 kg x 9.8 m/s^2 = 98 N. Therefore, the weight of the bag of groceries is about 100 N.

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• 40.

### The mass of a pet turtle that weighs 10 N is

• A.

• B.

• C.

• D.

• E.

None of these

Explanation
The weight of an object is equal to the force of gravity acting on it, which is given by the equation weight = mass * acceleration due to gravity. In this case, the turtle weighs 10 N, which means the force of gravity acting on it is 10 N. Since the acceleration due to gravity is approximately 9.8 m/s^2, we can rearrange the equation to solve for mass: mass = weight / acceleration due to gravity. Substituting the given values, we find that the mass of the turtle is approximately 1 kg.

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• 41.

### The force required to maintain an object at a constant velocity in free space is equal to

• A.

Zero

• B.

The mass of the object

• C.

The weight of the object

• D.

The force required to stop it

• E.

None of these

A. Zero
Explanation
The force required to maintain an object at a constant velocity in free space is equal to zero because according to Newton's first law of motion, an object at rest or in motion will remain in that state unless acted upon by an external force. In free space, where there is no friction or other forces acting on the object, no external force is needed to keep it moving at a constant velocity.

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• 42.

### An object following a straight-line path at constant speed

• A.

Has a net force acting upon it in the direction of motion

• B.

Has zero acceleration

• C.

Has no forces acting on it

• D.

None of these

B. Has zero acceleration
Explanation
An object following a straight-line path at constant speed has zero acceleration. This is because acceleration is the rate of change of velocity, and if the object is moving at a constant speed, its velocity is not changing. Therefore, there is no acceleration.

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• 43.

### A man weighing 800 N stands at rest on two bathroom scales so that his weight is distributed evenly over both scales. The reading on each scale is

• A.

200 N

• B.

400 N

• C.

800 N

• D.

1600 N

• E.

None of these

B. 400 N
Explanation
When the man stands at rest on two bathroom scales, his weight is distributed evenly over both scales. This means that each scale is supporting half of his weight. Since his weight is 800 N, each scale will read half of that, which is 400 N. Therefore, the reading on each scale is 400 N.

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• 44.

### Neglecting friction, a large block of ice and a small block of ice start sliding down an incline together. The heavier block will get to the bottom

• A.

Before the light block

• B.

After the light block

• C.

At the same time as the light block

C. At the same time as the light block
Explanation
The statement "Neglecting friction" implies that there is no external force slowing down the blocks. Since both blocks start sliding down the incline together, they will experience the same acceleration due to gravity. Therefore, they will reach the bottom of the incline at the same time. The weight or mass of the blocks does not affect their acceleration in this scenario.

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• 45.

### When a woman stands at rest with both feet on a scale, it reads 500 N. When she gently lifts one foot, the scale reads

• A.

Less than 500 N

• B.

More than 500 N

• C.

500 N

C. 500 N
Explanation
When a woman stands at rest with both feet on a scale, the scale reads 500 N because it is measuring the force exerted by her body on the scale. When she gently lifts one foot, the scale will still read 500 N because the force exerted by her body on the scale remains the same. The scale is measuring the total force exerted by the woman's body, not just the force exerted by her feet.

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• 46.

### A push on a 1-kg brick accelerates it. Neglecting friction, to equally accelerate a 10-kg brick, one would have to push with

• A.

Just as much force

• B.

10 times as much force

• C.

100 times as much force

• D.

One-tenth the amount of force

• E.

None of these

B. 10 times as much force
Explanation
To equally accelerate a 10-kg brick, one would have to push with 10 times as much force. This is because according to Newton's second law of motion, the force applied on an object is directly proportional to its mass and acceleration. In this case, the mass of the 10-kg brick is 10 times greater than the 1-kg brick, so to achieve the same acceleration, the force applied must also be 10 times greater.

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• 47.

### A 10-N block and a 1-N block lie on a horizontal frictionless table. To provide them with equal horizontal acceleration, we would have to push with

• A.

Equal forces on each block

• B.

10 times as much force on the heavier block

• C.

10 squared or 100 times as much force on the heavier block

• D.

1/10 as much force on the heavier block

• E.

None of these

B. 10 times as much force on the heavier block
Explanation
To provide equal horizontal acceleration to both blocks, we need to apply a force that overcomes the inertia of each block. The force required to overcome inertia is directly proportional to the mass of the object. Since the 10-N block is heavier than the 1-N block, it has more inertia and therefore requires a greater force to accelerate it. Therefore, we would have to push with 10 times as much force on the heavier block.

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• 48.

### A rocket becomes progressively easier to accelerate as it travels upward from the ground mainly because

• A.

Gravity becomes weaker with increased distance

• B.

The applied force on the rocket increases as burning of fuel progresses

• C.

The mass of the rocket decreases as fuel is burned

C. The mass of the rocket decreases as fuel is burned
Explanation
As fuel is burned, the mass of the rocket decreases. According to Newton's second law of motion, the force required to accelerate an object is inversely proportional to its mass. Therefore, as the mass of the rocket decreases, the force required to accelerate it decreases as well. This makes it easier for the rocket to accelerate as it travels upward from the ground.

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• 49.

### A rock is thrown vertically into the air. At the very top of its trajectory the net force on it is

• A.

Less than its weight

• B.

More than its weight

• C.

Equal to its weight

C. Equal to its weight
Explanation
At the very top of its trajectory, the rock is momentarily at rest before it starts to fall back down. This means that its acceleration is zero, and according to Newton's second law, the net force acting on an object is equal to its mass multiplied by its acceleration. Since the acceleration is zero, the net force on the rock must also be zero. However, the weight of an object is the force due to gravity acting on it, and it always acts downwards. Therefore, at the very top of its trajectory, the net force on the rock is equal to its weight.

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• 50.

### A rock is thrown vertically into the air. At the top of its path, its acceleration in meters per second per second is

• A.

Zero

• B.

9.8

• C.

Between 0 and 9.8

• D.

Greater than 9.8

B. 9.8
Explanation
When a rock is thrown vertically into the air, it experiences a constant acceleration due to gravity. This acceleration is always directed downwards and has a magnitude of 9.8 meters per second per second. At the top of its path, the rock momentarily comes to a stop before starting to fall back down. During this brief moment, the rock's velocity is zero, but its acceleration is still 9.8 meters per second per second, as gravity continues to act on it. Therefore, the correct answer is 9.8.

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• Current Version
• Mar 17, 2023
Quiz Edited by
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• Sep 12, 2012
Quiz Created by
Drtaylor

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