1.
When analyzing dynamics problems, free-body diagrams
Correct Answer
A. Should always be used
Explanation
Free-body diagrams should always be used when analyzing dynamics problems because they provide a visual representation of all the forces acting on an object. By including all the forces, both horizontal and vertical, the diagram helps to accurately analyze the motion and acceleration of the object. It is important to consider all the forces that are directly responsible for the acceleration, rather than including unrelated forces. Free-body diagrams are not limited to objects that are accelerating or in equilibrium, but are used in all dynamic situations.
2.
A force of 12 N acting in a direction [30ºE of S] is equivalent to which of the following pairs of forces acting simultaneously?
Correct Answer
E. 10 N [S], 6 N [E]
Explanation
The correct answer is 10 N [S], 6 N [E]. This is because the given force of 12 N acting in a direction [30ºE of S] can be resolved into two components: one along the south direction and one along the east direction. By using trigonometry, the south component is found to be 10 N and the east component is found to be 6 N. Therefore, the equivalent pair of forces is 10 N [S], 6 N [E].
3.
A hockey puck slides along an ice surface shortly after it has left the hockey stick that propelled it. Which of the following free-body diagrams best represents the hockey puck?
Correct Answer
D. D
Explanation
The correct free-body diagram for the hockey puck would show two forces acting on it: the force of gravity pulling it downwards and the force of friction opposing its motion along the ice surface. Diagram D accurately represents these two forces, with the force of gravity acting downwards and the force of friction acting opposite to the direction of the puck's motion.
4.
Study the free-body diagram below and choose the statement that best describes the object's motion.
Correct Answer
C. The object will accelerate northeast.
Explanation
The free-body diagram shows that there is a net force acting on the object in the northeast direction. Since there is a net force, Newton's second law states that the object will accelerate in the direction of the net force. Therefore, the object will accelerate northeast.
5.
Study the free-body diagram below and determine what additional force(s) would be required for the object to achieve uniform motion.
Correct Answer
E. 2 N [S] and 1 N [W]
Explanation
The free-body diagram shows a single force of 1 N in the west direction acting on the object. In order for the object to achieve uniform motion, there must be an additional force acting on it. The additional force should have a magnitude of 2 N and should be directed towards the south (S) direction. Additionally, there should be another force of 1 N directed towards the west (W) direction. These two additional forces, 2 N [S] and 1 N [W], when combined with the existing 1 N [W] force, will result in a net force of zero, allowing the object to achieve uniform motion.
6.
The free-body diagram below illustrates the forces acting on a 2.0-kg object as it is being pushed along a horizontal surface. What is the motion of the object?
Correct Answer
D. Moving at 3.1 m/s2
Explanation
The object is moving at 3.1 m/s^2 because there is an unbalanced force acting on it. The force of friction is opposing the force applied to the object, causing it to accelerate in the direction of the applied force. The acceleration can be calculated using Newton's second law, F = ma, where F is the net force and m is the mass of the object. Since the net force is non-zero, the object is accelerating and therefore moving.
7.
The free-body diagram of a 4.0-kg object is shown below. What additional force must act so that the object has an acceleration of 2.5 m/s^{2} [W]?
Correct Answer
C. 8.0 N [W]
Explanation
The free-body diagram shows that the object has a weight force of 14.0 N acting downwards. In order for the object to have an acceleration of 2.5 m/s2 in the westward direction, an additional force of equal magnitude but in the westward direction is required. The only option that matches this requirement is 8.0 N [W]. This force will counteract the friction and other forces acting on the object, allowing it to accelerate in the desired direction.
8.
Two identical arrows, A and B, are fired with different bows. The bow that fires arrow A exerts twice the average force as the bow that fires arrow B. Compare the accelerations of the two arrows.
Correct Answer
B. Arrow A will have twice the acceleration of arrow B.
Explanation
The acceleration of an object is directly proportional to the force applied to it and inversely proportional to its mass. Since both arrows have the same mass, the arrow fired with the bow exerting twice the average force will experience twice the acceleration. Therefore, Arrow A will have twice the acceleration of Arrow B.
9.
A hockey puck of mass 150 g is sliding south along the ice and slows at a rate of 1.2 m/s^{2}. What is the net force acting on the puck?
Correct Answer
D. 1.8 x 10-1 N [N]
Explanation
The net force acting on the puck can be calculated using Newton's second law, which states that force is equal to mass multiplied by acceleration. In this case, the mass of the puck is given as 150 g (or 0.15 kg) and the acceleration is given as 1.2 m/s^2. By multiplying these values together, we get a net force of 0.18 N. The direction of the force is north, as indicated by the [N] in the answer. Therefore, the correct answer is 1.8 x 10-1 N [N].
10.
Newton's third law essentially states
Correct Answer
E. Forces always occur in pairs
Explanation
Newton's third law states that forces always occur in pairs. This means that for every action, there is an equal and opposite reaction. When one object exerts a force on another object, the second object exerts a force of equal magnitude but in the opposite direction on the first object. This principle is fundamental in understanding the interactions between objects and is applicable in various scenarios, such as the recoil of a gun when a bullet is fired or the propulsion of a rocket through the expulsion of exhaust gases.
11.
Which of the following observations would be adequately explained by Newton's third law?
Correct Answer
B. A skater stands on a frictionless pond, tosses her bag in one direction and she accelerates in the opposite direction.
Explanation
When the skater tosses her bag in one direction, according to Newton's third law, there will be an equal and opposite reaction. This means that the skater will experience a force in the opposite direction, causing her to accelerate in the opposite direction. This observation can be adequately explained by Newton's third law, which states that for every action, there is an equal and opposite reaction.
12.
An object is pushed horizontally at a constant velocity. What can correctly be said about the forces acting on the object?
Correct Answer
B. The sum of all forces is zero.
Explanation
When an object is pushed horizontally at a constant velocity, it means that the object is experiencing a balanced force. 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 this case, the constant velocity indicates that the forces acting forward and backward are equal in magnitude and opposite in direction, resulting in a net force of zero. Therefore, the correct answer is that the sum of all forces is zero.
13.
Which of the following units is equivalent to a newton (N)?
Correct Answer
A. Kg·m/s2
Explanation
The unit kg·m/s2 is equivalent to a newton (N) because it represents the formula for force, which is mass (kg) multiplied by acceleration (m/s2). A newton is defined as the force required to accelerate a mass of one kilogram at a rate of one meter per second squared.
14.
Three masses are suspended vertically as shown in the diagram below. The system is accelerating upward. What is the relationship among the forces of tension?
Correct Answer
B. |FT1| > |FT2| > |FT3|
Explanation
The correct answer is |FT1| > |FT2| > |FT3|. In a system with multiple masses suspended vertically, the tension force decreases as you move down the system. This is because the force of gravity acting on each mass increases as you move down, and the tension force must counteract this force. Therefore, the top mass (FT1) experiences the greatest tension force, followed by the middle mass (FT2), and finally the bottom mass (FT3).
15.
The physical quantity, which is the measure of inertia, is
Correct Answer
E. Mass
Explanation
Mass is the physical quantity that measures inertia. Inertia refers to an object's resistance to changes in its motion. The greater the mass of an object, the greater its inertia, meaning it is more difficult to change its state of motion. Therefore, mass is the correct answer as it directly relates to the measure of inertia.
16.
Which law is in control of a spaceship which cruises through space at constant speed without using any fuel?
Correct Answer
A. Newton's first law
Explanation
Newton's first law, also known as the law of inertia, states that an object at rest will stay at rest and an object in motion will stay in motion with the same speed and direction, unless acted upon by an external force. In the case of a spaceship cruising through space at a constant speed without using any fuel, there are no external forces acting on it to change its state of motion. Therefore, the spaceship follows Newton's first law of motion.
17.
An object is hanging by two strings, A and B, anchored to the ceiling as in the diagram below. Each string holds the object in place with a force of 40 N at 30 degrees to the vertical. Determine the force of gravity required to keep the object motionless.
Correct Answer
C. 69 N [down]
Explanation
The object is being held in place by two strings, each exerting a force of 40 N at 30 degrees to the vertical. To keep the object motionless, the force of gravity must be equal to the sum of the forces exerted by the strings. Since the forces are at an angle, we can use trigonometry to find the vertical component of each force. The vertical component of each force is 40 N * sin(30°) = 20 N. Therefore, the total force of gravity required to keep the object motionless is 20 N + 20 N = 40 N. However, the answer choices are given in the downward direction, so the correct answer is 69 N [down].
18.
Describe the motion of the 2.0 kg mass below in the horizontal plane.
Correct Answer
A. The object accelerates at 1.5 m/s2 [right]
Explanation
The object accelerates at 1.5 m/s2 [right], indicating that there is a net force acting on the object in the right direction. This means that the object's velocity is increasing at a rate of 1.5 m/s2 in the right direction.