Physics Revision Quiz

1. Which of the following is a vector?

Temperature

Energy

Force

Time

Vectors are physical quantities with magnitude and direction. A force has both magnitude and direction (e.g. Weight = mass x gravitational acceleration and acts downwards).

Explanation

Vectors are physical quantities with magnitude and direction. A force has both magnitude and direction (e.g. Weight = mass x gravitational acceleration and acts downwards).

2. What is the resultant acceleration of the object shown below? (W is weight)

1.5 m/s2 to the left

1.5 m/s2 to the right

6 m/s2 to the left

6 m/s2 to the right

From the diagram it can be seen that weight is 20N, which means that the object's mass: mass = W / g mass = 20 / 10 = 2kg The resultant acceleration is in the horizontal direction, since the forces in the vertical direction are balanced. Resultant force = (9 + 6) - (5 + 7) = 3N Resultant force = ma 2 x a = 3 a = 1.5 m/s^2 to the right (in the direction of the resultant force)

Explanation

From the diagram it can be seen that weight is 20N, which means that the object's mass: mass = W / g mass = 20 / 10 = 2kg The resultant acceleration is in the horizontal direction, since the forces in the vertical direction are balanced. Resultant force = (9 + 6) - (5 + 7) = 3N Resultant force = ma 2 x a = 3 a = 1.5 m/s^2 to the right (in the direction of the resultant force)

3. Newton's First Law states that an object continues to be at rest or in a state of (a) __________ motion in a (b) __________ _____ unless acted on by a (c) _____________ ________. What is (a)?

The correct answer is "uniform". Newton's First Law states that an object continues to be at rest or in a state of uniform motion unless acted on by a force. This means that if an object is initially at rest, it will remain at rest, and if it is initially moving with a constant velocity, it will continue moving with the same velocity unless a force is applied to it.

Explanation

The correct answer is "uniform". Newton's First Law states that an object continues to be at rest or in a state of uniform motion unless acted on by a force. This means that if an object is initially at rest, it will remain at rest, and if it is initially moving with a constant velocity, it will continue moving with the same velocity unless a force is applied to it.

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4. Which of the following is true?

An object that does not move has no forces acting on it.

If an object accelerates, there is definitely a resultant force.

The normal reaction force and weight of an object are an example of an action-reaction pair of forces.

An object's inertia changes depending on where it is.

An object that does not move doesn't necessarily have no forces acting on it; it could be just that the forces are balanced.

Acceleration can only be brought about if there is a resultant force.

Action-reaction pairs of forces have to be of the same TYPE, so in fact these two are not a pair.

An object's inertia depends on its mass, which does not change no matter where it goes.

Explanation

An object that does not move doesn't necessarily have no forces acting on it; it could be just that the forces are balanced.

Acceleration can only be brought about if there is a resultant force.

Action-reaction pairs of forces have to be of the same TYPE, so in fact these two are not a pair.

An object's inertia depends on its mass, which does not change no matter where it goes.

5. A falling parachutist undergoes freefall acceleration. She experiences air resistance, which increases as her velocity increases. What will happen to the magnitude of air resistance as she falls (increases, decreases, remains the same)?

As she falls, the air resistance is smaller than her weight due to the small velocity at the start, and there is a resultant force that causes her to accelerate downwards. As her velocity increases, her air resistance will increase.

Explanation

As she falls, the air resistance is smaller than her weight due to the small velocity at the start, and there is a resultant force that causes her to accelerate downwards. As her velocity increases, her air resistance will increase.

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6. Which graph shows an object changing direction once?

A. The object moves at constant negative velocity before accelerating in the same direction (negative gradient) so its speed increases but it does not change direction.

B. The object starts from rest and accelerates in the negative direction with a negative velocity.

C. The object starts with a positive velocity, decelerates to zero velocity, then accelerates with a negative velocity (velocity changes from positive to negative).

D. The object starts with a positive velocity, decelerates to zero velocity, then accelerates to a maximum negative velocity. It then decelerates to zero again, and accelerates with a positive velocity (velocity changes from positive to negative to positive).

Explanation

A. The object moves at constant negative velocity before accelerating in the same direction (negative gradient) so its speed increases but it does not change direction.

B. The object starts from rest and accelerates in the negative direction with a negative velocity.

C. The object starts with a positive velocity, decelerates to zero velocity, then accelerates with a negative velocity (velocity changes from positive to negative).

D. The object starts with a positive velocity, decelerates to zero velocity, then accelerates to a maximum negative velocity. It then decelerates to zero again, and accelerates with a positive velocity (velocity changes from positive to negative to positive).

7. The same parachutist continues to fall downwards. What happens to her acceleration as she falls downwards (increases, decreases, remains the same)?

As she falls, her velocity increases, which causes the air resistance to increase. Since the air resistance opposes her weight, the resultant force decreases and hence her acceleration decreases.

Explanation

As she falls, her velocity increases, which causes the air resistance to increase. Since the air resistance opposes her weight, the resultant force decreases and hence her acceleration decreases.

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8. Newton's First Law states that an object continues to be at rest or in a state of uniform motion in a straight line unless acted on by a (c) _____________ ________. What is (c)?

Newton's First Law states that an object continues to be at rest or in a state of uniform motion in a straight line unless acted on by a resultant force, net force, or unbalanced force. These forces cause a change in the object's motion, either by starting it from rest, changing its speed or direction, or stopping it altogether. In other words, if there is no resultant force, net force, or unbalanced force acting on an object, it will continue to move in a straight line at a constant speed or remain at rest.

Explanation

Newton's First Law states that an object continues to be at rest or in a state of uniform motion in a straight line unless acted on by a resultant force, net force, or unbalanced force. These forces cause a change in the object's motion, either by starting it from rest, changing its speed or direction, or stopping it altogether. In other words, if there is no resultant force, net force, or unbalanced force acting on an object, it will continue to move in a straight line at a constant speed or remain at rest.

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9. What force(s) is/are acting on an object that is floating on the surface of the sea?

Tension

Upthrust

Weight

Normal contact force

A. Tension usually occurs when there is a spring or string.

B. Upthrust is the force of the water on the object that is keeping it afloat.

C. The earth still pulls the object toward itself.

D. There is no normal contact force in this case as there is no other surface that the object is in contact with.

Explanation

A. Tension usually occurs when there is a spring or string.

B. Upthrust is the force of the water on the object that is keeping it afloat.

C. The earth still pulls the object toward itself.

D. There is no normal contact force in this case as there is no other surface that the object is in contact with.

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10. Newton's First Law states that an object continues to be at rest or in a state of uniform motion in a (b) __________ _____ unless acted on by a (c) _____________ ________. What is (b)?

Newton's First Law states that an object continues to be at rest or in a state of uniform motion in a straight line unless acted on by a force.

Explanation

Newton's First Law states that an object continues to be at rest or in a state of uniform motion in a straight line unless acted on by a force.

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11. What is the magnitude of the resultant force on the block below?

In the vertical direction, the resultant force is 4N. To find the overall resultant force, we can add the vectors as shown below:

x² = 3² + 4²

x = 5

Explanation

In the vertical direction, the resultant force is 4N. To find the overall resultant force, we can add the vectors as shown below:

x² = 3² + 4²

x = 5

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12. What is the SI unit of electric current, which measures the flow of electric charge in a circuit?

Volts

Watts

Amperes (A)

Ohms

Amperes (A): This is the correct answer. The ampere, often referred to as an amp, is the SI unit of electric current. It measures the flow of electric charge through a conductor or circuit. One ampere is defined as one coulomb of charge passing through a point in a circuit per second.

Explanation

Amperes (A): This is the correct answer. The ampere, often referred to as an amp, is the SI unit of electric current. It measures the flow of electric charge through a conductor or circuit. One ampere is defined as one coulomb of charge passing through a point in a circuit per second.

13. The image below shows a truck engine pulling a trailer which is attached to it by a towbar, and the engine thrust is providing an acceleration of 0.1m/s². The resistive force on the trailer is 5N. Using a free body diagram of the trailer, find the tension in the towbar.

The acceleration is to the right, which means that resultant force is also in the same direction. From the diagram, resultant force = T - R ma = T - R T = ma + R T = (1000 x 0.10) + 5 T = 105N

Explanation

The acceleration is to the right, which means that resultant force is also in the same direction. From the diagram, resultant force = T - R ma = T - R T = ma + R T = (1000 x 0.10) + 5 T = 105N

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14. A ball is thrown vertically upwards with an initial velocity of 30.0 m/s from the top of a building that is 15.0m high. What is the total time it takes before it reaches the ground? (take g = 10m/s²)

Taking upwards as positive,

u = 30.0 m/s

s = -15.0m (the ball ends up 15.0m downwards which is negative)

a = -10m/s (this acts downwards which is negative)

t = ?

v = ?

Using the equation s = ut + 0.5at²,

-15.0 = (30.0)t + 0.5(-10)(t²)

-15.0 = (30.0)t + 0.5(-10)(t^2)

5t² + 30.0t + 15.0 = 0

t² + 6t + 3 = 0

t = 6.5s (2sf)

Explanation

Taking upwards as positive,

u = 30.0 m/s

s = -15.0m (the ball ends up 15.0m downwards which is negative)

a = -10m/s (this acts downwards which is negative)

t = ?

v = ?

Using the equation s = ut + 0.5at²,

-15.0 = (30.0)t + 0.5(-10)(t²)

-15.0 = (30.0)t + 0.5(-10)(t^2)

5t² + 30.0t + 15.0 = 0

t² + 6t + 3 = 0

t = 6.5s (2sf)

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15. What will happen to her velocity eventually?

As her air resistance increases, it will come to a point where the air resistance is equal to her weight and there is no more resultant force. SInce there is no resultant force any longer, she will continue in a state of uniform motion in a straight line (downwards), so her velocity remains the same (this is called the terminal velocity).

The air resistance will not increase anymore since the velocity is not increasing.

Explanation

As her air resistance increases, it will come to a point where the air resistance is equal to her weight and there is no more resultant force. SInce there is no resultant force any longer, she will continue in a state of uniform motion in a straight line (downwards), so her velocity remains the same (this is called the terminal velocity).

The air resistance will not increase anymore since the velocity is not increasing.

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