Question 1

A racquetball is dropped from a height of one meter. It bounces off the floor and rises to a height of 0.8 m. The collision with the floor was
A) an elastic collision.
B) a partially inelastic collision.
C) a perfectly inelastic collision.
D) impossible to tell without knowing the mass of the ball.

Accepted Answer

A perfectly elastic collision would result in the ball returning to its original height, while a perfectly inelastic collision would result in the ball sticking to the floor. Since the ball bounces back up to a diminished height, it must have lost some kinetic energy during the collision, making it a partially inelastic collision. The mass of the ball is not necessary to determine the type of collision.

Question 2

A bullet of mass 0.010 kg and speed of 200 m/s is brought to rest in a wooden block after penetrating a distance of 0.10 m. This process takes 0.02 second. The magnitude of the impulse delivered to the bullet by the block during this time is
A) zero.
B) 0.98 N.
C) 1.0 Ns.
D) 2.0 Ns.
E) 4.0 Ns.

Accepted Answer

Impulse is the change in momentum. The initial momentum is 0.010 kg * 200 m/s = 2.0 kg*m/s, and the final momentum is 0 since the bullet is at rest. Thus, the impulse is 2.0 Ns.

Question 3

A box is moved 10 m across a smooth floor by a force F making a downward angle with the floor, so that there is effectively a 4 N force acting parallel to the floor in the direction of motion and a 3 N force acting perpendicular to the floor. The force F acts for 20 seconds. The impulse delivered to the box by the floor during this process has magnitude
A) 100 Ns.
B) 80 Ns.
C) 60 Ns.
D) zero.
E) Can't tell without knowing the weight of the box.

Accepted Answer

The answer of A box is moved 10 m across...

Question 4

If the speed of a car is tripled, the impulse required to stop the car changes by a factor of
A) 9.
B) 3.
C) 1.
D) 1/3.
E) 1/9.

Accepted Answer

The answer of If the speed of a car is...

Question 5

A bullet is fired into a wall and comes to rest. Considering only the bullet as the system we can say that
A) the total kinetic energy is conserved.
B) the momentum is conserved.
C) neither total kinetic energy nor momentum is conserved.
D) both total kinetic energy and momentum are conserved.

Accepted Answer

The total kinetic energy is not conserved because it is converted into other forms of energy (such as heat and sound) when the bullet stops. Momentum is not conserved for the bullet alone because external forces (from the wall) act on it, bringing it to a stop.

Question 6

Suppose two boys are trapped on the ice atop a frozen pond, and that the ice is completely frictionless. The boys are initially at rest, but they do have a baseball. They begin to play catch with the ball. Which of these is true?
A) The boys only move while the ball is in the air.
B) They will be stuck on the ice until rescued.
C) The more times they throw and catch the ball, the faster they will get to shore.
D) If after a few throws the ball is not caught and rolls away, the boys will be stuck on the ice.

Accepted Answer

When the boys throw the baseball to each other, they exert a force on the ball, and the ball exerts an equal and opposite force on them, causing them to move in opposite directions due to Newton's third law of motion. Each throw and catch will result in a small movement, and over time, these movements will add up, allowing them to move closer to shore. The frictionless surface ensures that they will continue moving after each throw and catch, gradually increasing their distance from their original positions.

Question 7

Collisions between which pairs of objects is likely to be most nearly elastic?
A) A steel ball and a cotton ball
B) Two steel balls
C) A steel ball and a baseball
D) Two baseballs

Accepted Answer

Elastic collisions are those in which the objects bounce off each other without any loss of kinetic energy. When two objects have the same material, such as in the case of two steel balls, then the collision is likely to be most nearly elastic. In contrast, when one object is much softer than the other, such as in the case of a steel ball and a cotton ball or a steel ball and a baseball, then the collision will not be as nearly elastic because the softer object will absorb some of the kinetic energy. Therefore, the collision between two steel balls is the most likely to be nearly elastic.

Question 8

Although Newton's second law, F = ma, is valid for collisions, it is difficult to use it generally in this form for collisions because
A) the acceleration is too small.
B) the force F is not constant.
C) the acceleration occurs during a time interval too short to measure easily.
D) the acceleration is too small and the force F is not constant.
E) the force F is not constant and the acceleration occurs during a time interval too short to measure easily.

Accepted Answer

In collisions, the force F is usually not constant and the acceleration occurs over a very short time interval. This makes it difficult to measure the acceleration accurately, and hence it is difficult to use Newton's second law in its original form. Therefore, alternative methods and equations, such as impulse-momentum theorem and conservation of momentum, are used to analyze collisions.

Question 9

During a collision, which of these is an indication that the total momentum has changed?
A) Heat is generated.
B) Deformation occurs.
C) Sound is produced.
D) Heat is generated, deformation occurs, and sound is produced.
E) None of these are correct.

Accepted Answer

The total momentum of a system is conserved during a collision, assuming no external forces act on the system. Heat generation, deformation, and sound production are forms of energy transformation and do not indicate a change in total momentum.

Question 10

Suppose a ball is dropped from shoulder height, falls, makes a perfectly elastic collision with the floor, and rebounds to shoulder height. Compare the magnitudes of the impulses delivered to the ball by gravity and by the floor during this entire motion.
A) The impulse delivered by the floor is half as large as the impulse delivered by gravity.
B) The impulse delivered by the floor is twice as large as the impulse delivered by gravity.
C) The two impulses have the same magnitude.
D) The floor delivers an upward impulse, but gravity does not deliver a total impulse.

Accepted Answer

According to the law of conservation of momentum, the impulse imparted on the ball by gravity must be equal and opposite to the impulse imparted on the ball by the floor. Since the ball returns to its original height, the magnitudes of these two impulses must be equal, so the answer is C.

Question 11

A box is pushed across a rough horizontal floor by a force acting parallel to the floor in the direction of motion. A force providing no impulse during the motion is
A) gravity.
B) friction.
C) the applied force.
D) none of these.

Accepted Answer

The answer of A box is pushed across a rough...

Question 12

Moving at a constant speed, an elevator lifts a 1000 N package 10 meters in 3 seconds. During this time, the impulse delivered to the package by the elevator floor is
A) 10,000 Ns up.
B) 3,000 Ns up.
C) 10,000 Nm up.
D) zero.

Accepted Answer

The impulse delivered to an object is given by the equation:

Impulse = Force x Time

Since the package is lifted at a constant speed, that means the net force acting on the package is zero (otherwise, the package would be accelerating). Therefore, the only force acting on the package is its weight, which is 1000 N.

Since the package is lifted a distance of 10 meters, the work done by the force of gravity is:

Work = Force x Distance x cos(theta)

where theta is the angle between the force and the direction of motion. Since the force of gravity is downwards and the package is lifted upwards, theta is 180 degrees, so cos(theta) = -1.

Therefore, the work done by gravity is:

Work = (1000 N) x (10 m) x (-1) = -10,000 J

Since the only force acting on the package is its weight, and the work done by gravity is negative, the elevator must do an equal amount of positive work in order to lift the package at a constant speed. Therefore, the impulse delivered by the elevator is:

Impulse = Force x Time = (1000 N) x (3 s) = 3000 Ns up

Therefore, the correct answer is B.

Question 13

A box is pushed eastward across a rough horizontal floor by a force acting parallel to the floor. A force providing an impulse directed westward on the body is
A) gravity.
B) the applied force.
C) friction.
D) normal reaction force of floor upward on body.
E) a fictitious force.

Accepted Answer

The only force acting opposite to the direction of motion is friction. Therefore, the force providing an impulse directed westward on the body must be friction.

Question 14

If a force acts on an object, the impulse will be
A) zero if the force is applied perpendicular to the momentum object.
B) zero if the force is in the opposite direction of the velocity of the object.
C) zero if the speed of the object does not change.
D) nonzero in all situations.

Accepted Answer

Impulse is equal to the force applied multiplied by the time it acts on the object. Therefore, unless the force applied is zero, impulse will always be non-zero.

Question 15

During a collision, which of these is an indication that the total kinetic energy has changed?
A) Heat is generated.
B) Deformation occurs.
C) Sound is produced.
D) Heat is generated, deformation occurs, and sound is produced.
E) None of these are correct.

Accepted Answer

The generation of heat, deformation, and production of sound are all indications that the total kinetic energy has changed during a collision. The kinetic energy is converted into other forms of energy such as heat and sound, and the deformation of the objects involved. Therefore, option D is the best choice as it includes all three of these indications.

Question 16

A car moving east collides with a truck moving north. The vehicles have the same speed but the truck has twice the mass of the car. If the vehicles stick together after the collision, what is the path followed by the vehicles after the collision? 
A) A
B) B
C) C
D) D
E) E

Accepted Answer

The answer of A car moving east collides with a...

Question 17

The principle that total momentum does not change during a brief collision is a result of
A) the definition of the kilogram.
B) the definition of the newton.
C) Newton's first law and Newton's second law.
D) Newton's first law and Newton's third law.
E) Newton's second law and Newton's third law.

Accepted Answer

The principle of conservation of momentum during a collision is derived from Newton's second law (force equals mass times acceleration) and Newton's third law (for every action, there is an equal and opposite reaction). These laws together imply that the total momentum of a closed system remains constant if no external forces act on it.

Question 18

A 3 kg block, initially moving due east at 6 m/s, is acted upon by an impulse having magnitude 6 Ns and direction due west. The final velocity of the block is
A) 8 m/s east.
B) 4 m/s east.
C) 4 m/s west.
D) 8 m/s west.

Accepted Answer

The impulse changes the momentum of the block. The impulse is given by $I = F\Delta t = \Delta p = m\Delta v$, where $I$ is the impulse, $F$ is the force, $\Delta t$ is the time interval, $\Delta p$ is the change in momentum, $m$ is the mass, and $\Delta v$ is the change in velocity. Given $I = 6\, \text{Ns}$ west, and the initial velocity is $6\, \text{m/s}$ east, the change in velocity can be calculated as $\Delta v = \frac{I}{m} = \frac{6}{3} = 2\, \text{m/s}$ to the west. Therefore, the final velocity is $6\, \text{m/s} - 2\, \text{m/s} = 4\, \text{m/s}$ east.

Question 19

A painter of mass 80 kg climbs 3.0 m up a ladder. The painter has gained momentum in the amount of
A) 240 J.
B) 784 J.
C) 2352 J.
D) Can't say without knowing his velocity change (if any)

Accepted Answer

Momentum is a vector quantity defined as the product of an object's mass and its velocity (p = mv). The information given describes a change in gravitational potential energy (mgh), not a change in momentum. To calculate or discuss a change in momentum, we need information about the velocity change, which is not provided.

Question 20

A friend drops a package to you from a window 16 feet above where you first catch it. It drops an additional 3 feet as you bring it to a stop with a constant force. In order to calculate the force required, you need
A) the time it takes for you to stop the package.
B) the mass of the package.
C) no additional information.

Accepted Answer

The force required to bring an object to a stop with a constant force is dependent on the mass of the object, so knowing the mass of the package is necessary to calculate the force required. The time it takes to stop the package is not needed for this calculation and the additional distance it drops does not affect the force required.

Quiz 7: Momentum and Impulse

A racquetball is dropped from a height of one meter. It bounces off the floor and rises to a height of 0.8 m. The collision with the floor was

A bullet of mass 0.010 kg and speed of 200 m/s is brought to rest in a wooden block after penetrating a distance of 0.10 m. This process takes 0.02 second. The magnitude of the impulse delivered to the bullet by the block during this time is

If the speed of a car is tripled, the impulse required to stop the car changes by a factor of

A bullet is fired into a wall and comes to rest. Considering only the bullet as the system we can say that

Suppose two boys are trapped on the ice atop a frozen pond, and that the ice is completely frictionless. The boys are initially at rest, but they do have a baseball. They begin to play catch with the ball. Which of these is true?

Collisions between which pairs of objects is likely to be most nearly elastic?

Although Newton's second law, F = ma, is valid for collisions, it is difficult to use it generally in this form for collisions because

During a collision, which of these is an indication that the total momentum has changed?

Suppose a ball is dropped from shoulder height, falls, makes a perfectly elastic collision with the floor, and rebounds to shoulder height. Compare the magnitudes of the impulses delivered to the ball by gravity and by the floor during this entire motion.

A box is pushed across a rough horizontal floor by a force acting parallel to the floor in the direction of motion. A force providing no impulse during the motion is

Moving at a constant speed, an elevator lifts a 1000 N package 10 meters in 3 seconds. During this time, the impulse delivered to the package by the elevator floor is

A box is pushed eastward across a rough horizontal floor by a force acting parallel to the floor. A force providing an impulse directed westward on the body is

If a force acts on an object, the impulse will be

During a collision, which of these is an indication that the total kinetic energy has changed?

A car moving east collides with a truck moving north. The vehicles have the same speed but the truck has twice the mass of the car. If the vehicles stick together after the collision, what is the path followed by the vehicles after the collision?

The principle that total momentum does not change during a brief collision is a result of

A 3 kg block, initially moving due east at 6 m/s, is acted upon by an impulse having magnitude 6 Ns and direction due west. The final velocity of the block is

A painter of mass 80 kg climbs 3.0 m up a ladder. The painter has gained momentum in the amount of

A friend drops a package to you from a window 16 feet above where you first catch it. It drops an additional 3 feet as you bring it to a stop with a constant force. In order to calculate the force required, you need