Question 1

Which one of the following free-body diagrams best represents the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward with an unchanging velocity? _f is the force of the floor on the person and _g is the force of gravity on the person. A) B) C) D) E)

Accepted Answer

In this scenario, the elevator is traveling upward at an unchanging velocity, which means that the acceleration is zero. The forces acting on the person in the elevator are his weight (due to gravity) and the normal force (or upward force) provided by the elevator floor. Since the elevator is not accelerating, the net force on the person must be zero. Therefore, the normal force must be equal in magnitude and opposite in direction to the weight. Choice B correctly represents these forces with the correct magnitudes and directions.

Question 2

Two objects have masses m and 5m, respectively. They both are placed side by side on a frictionless inclined plane and allowed to slide down from rest.
A) It takes the lighter object 5 times longer to reach the bottom of the incline than the heavier object.
B) It takes the lighter object 10 times longer to reach the bottom of the incline than the heavier object.
C) It takes the heavier object 5 times longer to reach the bottom of the incline than the lighter object.
D) It takes the heavier object 10 times longer to reach the bottom of the incline than the lighter object.
E) The two objects reach the bottom of the incline at the same time.

Accepted Answer

The acceleration of an object down an inclined plane due to gravity is independent of its mass. Therefore, both objects, regardless of their mass difference, will reach the bottom of the incline at the same time in the absence of friction.

Question 3

A string is attached to the rear-view mirror of a car. A ball is hanging at the other end of the string. The car is driving around in a circle, at a constant speed. Which of the following lists gives all of the forces directly acting on the ball?
A) tension and gravity
B) tension
C) tension, gravity, and the centripetal force
D) tension, gravity, the centripetal force, and friction

Accepted Answer

The only forces acting on the ball are tension (from the string) and gravity. The centripetal force is not a separate force, but rather the net force that is required to keep the ball moving in a circular path. Friction is likely present, but it is not directly acting on the ball itself.

Question 4

Two objects are connected by a very light flexible string as shown in the figure, where M = 0.60 kg and m = 0.40 kg. You can ignore friction and the mass of the pulley.  
(a) Draw free-body diagrams for each object.
(b) Calculate the magnitude of the acceleration of each object.
(c) Calculate the tension in the string.

Accepted Answer

The answer of Two objects are connected by a very...

Question 5

Two weights are connected by a massless wire and pulled upward with a constant speed of 1.50 m/s by a vertical pull P. The tension in the wire is T (see figure). Which one of the following relationships between T and P must be true? 
A) T > P
B) T = P
C) P + T = 125 N
D) P = T + 25 N
E) P = T + 100 N

Accepted Answer

The answer of Two weights are connected by a massless...

Question 6

If you swing a bucket of water fast enough in a vertical circle, at the highest point the water does not spill out because an outward force balances the pull of gravity on the water.

Accepted Answer

At the highest point, the water does not spill out because the centripetal force required to keep it in circular motion is provided by the force of gravity acting on the water, not an outward force.

Question 7

A box slides down a frictionless plane inclined at an angle θ above the horizontal. The gravitational force on the box is directed
A) parallel to the plane in the same direction as the movement of the box.
B) parallel to the plane in the opposite direction as the movement of the box.
C) perpendicular to the plane.
D) vertically.
E) at an angle θ below the inclined plane.

Accepted Answer

The gravitational force is always directed vertically downwards, regardless of the incline of the plane. Therefore, the correct answer is option D.

Question 8

A brick is resting on a rough incline as shown in the figure. The friction force acting on the brick, along the incline, is 
A) zero.
B) equal to the weight of the brick.
C) greater than the weight of the brick.
D) less than the weight of the brick.

Accepted Answer

The friction force acting on the brick is opposing the motion of the brick along the incline. Since the brick is at rest, the net force acting on it is zero. This means that the friction force must be equal and opposite to the component of the weight of the brick that is parallel to the incline. The weight of the brick can be resolved into two components: one perpendicular to the incline (normal force) and the other parallel to the incline (mg*sinθ). Since the brick is not moving, the friction force must be equal to the parallel component of the weight, which is mg*sinθ. As sinθ is less than 1, the friction force is less than the weight of the brick. Therefore, the correct choice is D.

Question 9

A 60.0-kg person rides in elevator while standing on a scale. The elevator is traveling downward but slowing down at a rate of 2.00 m/s². The reading on the scale is closest to A) 589 N. B) 708 N. C) 469 N. D) 120 N. E) 349 N.

Accepted Answer

When the elevator is slowing down while moving downward, it is experiencing an upward acceleration. The apparent weight is calculated by adding the product of mass and acceleration to the gravitational force: $ W = m(g + a) = 60.0 \, \text{kg} \times (9.8 \, \text{m/s}^2 + 2.0 \, \text{m/s}^2) = 708 \, \text{N} $.

Question 10

Which one of the following free-body diagrams best represents the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward but is gradually slowing down at a rate of 9 m/s2? _f is the force of the floor on the person and _g is the force of gravity on the person. A) B) C) D) E)

Accepted Answer

The answer of Which one of the following free-body diagrams...

Question 11

When a parachutist jumps from an airplane, he eventually reaches a constant speed, called the terminal speed. Once he has reached terminal speed
A) his acceleration is equal to g.
B) the force of air drag on him is equal to zero.
C) the force of air drag on him is equal to g.
D) his speed is equal to g.
E) the force of air drag on him is equal to his weight.

Accepted Answer

When a parachutist reaches terminal speed, the force of air drag is equal to his weight, resulting in a net force of zero and thus no further acceleration.

Question 12

Suppose the force of the air drag on an object is proportional to the speed of the object and in the direction opposite the object's velocity. If you throw an object upward, the magnitude of its acceleration is greatest
A) right after the object is released.
B) at the top of its trajectory.
C) The acceleration of the object is the same throughout the entire trajectory.

Accepted Answer

The force of air drag is greatest immediately after the object is released because at this point the object is moving at its greatest speed. As the object moves upward, the force of air drag will decrease as the speed of the object decreases, resulting in a lower acceleration. At the top of its trajectory, the object momentarily stops moving upward and begins to fall back down, so its acceleration is zero at this point.

Question 13

A 60.0-kg person rides in an elevator while standing on a scale. The scale reads 400 N. The acceleration of the elevator is closest to A) 3.13 m/s² downward. B) 6.67 m/s² downward. C) zero. D) 9.80 m/s² downward. E) 6.67 m/s²upward.

Accepted Answer

The normal force (scale reading) is 400 N. The gravitational force is 60.0 kg * 9.8 m/s² = 588 N. The net force is 400 N - 588 N = -188 N, indicating downward acceleration. Using F = ma, -188 N = 60.0 kg * a, gives a ≈ 3.13 m/s² downward.

Question 14

Two unequal masses M and m (M > m) are connected by a light cord passing over a pulley of negligible mass, as shown in the figure. When released, the system accelerates. Friction is negligible. Which figure below gives the correct free-body force diagrams for the two masses in the moving system? 
A)

B)

C)

D)

Accepted Answer

For mass M, the only force acting on it is the tension in the rope pulling upward. For mass m, the force of gravity is pulling down and the tension in the rope is pulling up. As the system moves, the tension remains constant throughout the rope, so the diagrams in choices A and D, which show different tensions on each side of the pulley, are incorrect. Choice B shows gravity pulling up on mass m, which is incorrect. Therefore, the correct force diagrams are shown in choice C.

Question 15

A woman is straining to lift a large crate, without success because it is too heavy. We denote the forces on the crate as follows: P is the upward force the woman exerts on the crate, C is the vertical contact force exerted on the crate by the floor, and W is the weight of the crate. How are the magnitudes of these forces related while the woman is trying unsuccessfully to lift the crate?
A) P + C = W
B) P + C < W
C) P + C > W
D) P = C

Accepted Answer

P + C = W. When the woman is trying to lift the crate but is unsuccessful, the crate does not move, indicating it is in static equilibrium. Therefore, the sum of the upward forces (P + C) must equal the downward force (W) due to gravity.

Question 16

A crate is sliding down an inclined ramp at a constant speed of 0.55 m/s. The vector sum of all the forces acting on this crate must point down the ramp.

Accepted Answer

If the crate is sliding down the ramp at a constant speed, the forces of friction and gravity must be balanced. Therefore, the vector sum of all the forces must be zero, not necessarily pointing down the ramp.

Question 17

Suppose a highway curve is properly banked to eliminate friction for a speed of 45 mph. If your tires were bald and you wanted to avoid sliding on the road, you would have to drive
A) somewhat below 45 mph.
B) somewhat above 45 mph.
C) at exactly 45 mph.

Accepted Answer

The answer of Suppose a highway curve is properly banked...

Question 18

Two bodies P and Q on a smooth horizontal surface are connected by a light cord. The mass of P is greater than that of Q. A horizontal force  (of magnitude F) is applied to Q as shown in the figure, accelerating the bodies to the right. The magnitude of the force exerted by the connecting cord on body P will be

A) zero.
B) less than F but not zero.
C) equal to F.
D) greater than F.

Accepted Answer

Since the surface is smooth, there is no horizontal frictional force acting on either body. Thus, the only horizontal force on body P is the force exerted by the connecting cord. This force, by Newton's third law, is equal in magnitude but opposite in direction to the force exerted by body P on the cord. Since body P is more massive, it will experience a smaller acceleration than body Q. Therefore, the tension in the cord will be less than the applied force F but not zero. Thus, the correct answer is B: less than F but not zero.

Question 19

Two objects having masses m₁ and m₂ are connected to each other as shown in the figure and are released from rest. There is no friction on the table surface or in the pulley. The masses of the pulley and the string connecting the objects are completely negligible. What must be true about the tension T in the string just after the objects are released? A) T = m₂g B) T > m₂g C) T < m₂g D) T = m₁g E) T > m₁g

Accepted Answer

The answer of Two objects having masses m₁ and m₂...

Question 20

A 615 N student standing on a scale in an elevator notices that the scale reads 645 N. From this information, the student knows that the elevator must be moving
A) downward.
B) upward.
C) You cannot tell if it is moving upward or downward.

Accepted Answer

The answer of A 615 N student standing on a...

Quiz 5: Applying Newtons Laws

Which one of the following free-body diagrams best represents the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward with an unchanging velocity? _f is the force of the floor on the person and _g is the force of gravity on the person.

Two objects have masses m and 5m, respectively. They both are placed side by side on a frictionless inclined plane and allowed to slide down from rest.

A string is attached to the rear-view mirror of a car. A ball is hanging at the other end of the string. The car is driving around in a circle, at a constant speed. Which of the following lists gives all of the forces directly acting on the ball?

Two weights are connected by a massless wire and pulled upward with a constant speed of 1.50 m/s by a vertical pull P. The tension in the wire is T (see figure) . Which one of the following relationships between T and P must be true?

If you swing a bucket of water fast enough in a vertical circle, at the highest point the water does not spill out because an outward force balances the pull of gravity on the water.

A box slides down a frictionless plane inclined at an angle θ above the horizontal. The gravitational force on the box is directed

A brick is resting on a rough incline as shown in the figure. The friction force acting on the brick, along the incline, is

A 60.0-kg person rides in elevator while standing on a scale. The elevator is traveling downward but slowing down at a rate of 2.00 m/s². The reading on the scale is closest to

When a parachutist jumps from an airplane, he eventually reaches a constant speed, called the terminal speed. Once he has reached terminal speed

Suppose the force of the air drag on an object is proportional to the speed of the object and in the direction opposite the object's velocity. If you throw an object upward, the magnitude of its acceleration is greatest

A 60.0-kg person rides in an elevator while standing on a scale. The scale reads 400 N. The acceleration of the elevator is closest to

Two unequal masses M and m (M > m) are connected by a light cord passing over a pulley of negligible mass, as shown in the figure. When released, the system accelerates. Friction is negligible. Which figure below gives the correct free-body force diagrams for the two masses in the moving system?

A crate is sliding down an inclined ramp at a constant speed of 0.55 m/s. The vector sum of all the forces acting on this crate must point down the ramp.

Suppose a highway curve is properly banked to eliminate friction for a speed of 45 mph. If your tires were bald and you wanted to avoid sliding on the road, you would have to drive

A 615 N student standing on a scale in an elevator notices that the scale reads 645 N. From this information, the student knows that the elevator must be moving

Quiz 5: Applying Newtons Laws

Which one of the following free-body diagrams best represents the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward with an unchanging velocity? f is the force of the floor on the person and g is the force of gravity on the person.

Two objects have masses m and 5m, respectively. They both are placed side by side on a frictionless inclined plane and allowed to slide down from rest.

A string is attached to the rear-view mirror of a car. A ball is hanging at the other end of the string. The car is driving around in a circle, at a constant speed. Which of the following lists gives all of the forces directly acting on the ball?

Two weights are connected by a massless wire and pulled upward with a constant speed of 1.50 m/s by a vertical pull P. The tension in the wire is T (see figure) . Which one of the following relationships between T and P must be true?

If you swing a bucket of water fast enough in a vertical circle, at the highest point the water does not spill out because an outward force balances the pull of gravity on the water.

A box slides down a frictionless plane inclined at an angle θ above the horizontal. The gravitational force on the box is directed

A brick is resting on a rough incline as shown in the figure. The friction force acting on the brick, along the incline, is

A 60.0-kg person rides in elevator while standing on a scale. The elevator is traveling downward but slowing down at a rate of 2.00 m/s2. The reading on the scale is closest to

When a parachutist jumps from an airplane, he eventually reaches a constant speed, called the terminal speed. Once he has reached terminal speed

Suppose the force of the air drag on an object is proportional to the speed of the object and in the direction opposite the object's velocity. If you throw an object upward, the magnitude of its acceleration is greatest

A 60.0-kg person rides in an elevator while standing on a scale. The scale reads 400 N. The acceleration of the elevator is closest to

Two unequal masses M and m (M > m) are connected by a light cord passing over a pulley of negligible mass, as shown in the figure. When released, the system accelerates. Friction is negligible. Which figure below gives the correct free-body force diagrams for the two masses in the moving system?

A crate is sliding down an inclined ramp at a constant speed of 0.55 m/s. The vector sum of all the forces acting on this crate must point down the ramp.

Suppose a highway curve is properly banked to eliminate friction for a speed of 45 mph. If your tires were bald and you wanted to avoid sliding on the road, you would have to drive

A 615 N student standing on a scale in an elevator notices that the scale reads 645 N. From this information, the student knows that the elevator must be moving

Which one of the following free-body diagrams best represents the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward with an unchanging velocity? _f is the force of the floor on the person and _g is the force of gravity on the person.

A 60.0-kg person rides in elevator while standing on a scale. The elevator is traveling downward but slowing down at a rate of 2.00 m/s². The reading on the scale is closest to