Question 1

Recoil is noticeable if we throw a heavy ball while standing on roller skates. If instead we go through the motions of throwing the ball but hold onto it, our net recoil will be

Accepted Answer

According to the law of conservation of momentum, the total momentum of an isolated system remains constant. In this case, the system includes the person on roller skates and the ball. When the person throws the ball, they exert a force on it, which causes the ball to move in one direction and the person to move in the opposite direction. This results in a net momentum of zero for the system. However, if the person goes through the motions of throwing the ball but does not release it, there is no change in the momentum of the system. Therefore, there is no recoil and the net momentum remains zero. Hence, the answer is A.

Question 2

The force that accelerates a rocket in outer space is exerted on the rocket by the

Accepted Answer

The force that accelerates a rocket in outer space is exerted by the exhaust gases. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. The action of the exhaust gases being expelled out of the rocket's engine at high speed produces a reaction force that propels the rocket forward.

Question 3

A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish at rest. The speed of the larger fish after lunch is

Accepted Answer

The conservation of momentum can be used to solve the problem. Before lunch, the total momentum of the system is (5 kg)(1 m/s) + (1 kg)(0 m/s) = 5 kg·m/s. After lunch, the total momentum is (6 kg)(v), where v is the speed of the larger fish. Since momentum is conserved, we have 5 kg·m/s = 6 kg·v, which gives v = 5/6 m/s. Therefore, the answer is (C).

Question 4

According to the impulse-momentum equation Ft = change in (mv), a bungee jumper in fall has momentum which is reduced by the force F exerted by the bungee cord. If m is the mass of the jumper, then v in the equation is the speed of the

Accepted Answer

In the impulse-momentum equation Ft = Δ(mv), "v" represents the velocity of the object whose momentum is changing, which in this context is the bungee jumper. The equation does not concern the speed of the cord.

Question 5

A 1-kg chunk of putty moving at 1 m/s collides with and sticks to a 5-kg bowling ball that is initially at rest. The bowling ball and putty are then set in motion with a speed of

Accepted Answer

The law of conservation of momentum states that the total momentum before the collision is equal to the total momentum after the collision. Before the collision, the momentum is (1 kg * 1 m/s) + (5 kg * 0 m/s) = 1 kg*m/s. After the collision, the combined mass is 6 kg, so the speed is 1 kg*m/s / 6 kg = 1/6 m/s.

Question 6

A heavy truck and a small car rolling down a hill at the same speed are forced to stop in the same amount of time. Compared to the force that stops the car, the force needed to stop the truck is

Accepted Answer

The force needed to stop the truck is greater because the truck has a larger mass than the car. According to Newton's second law, force is equal to mass times acceleration (F=ma). To stop both vehicles in the same amount of time, a larger force must be applied to the truck due to its greater mass.

Question 7

A 30-kg girl and a 25-kg boy face each other on friction-free roller blades. The girl pushes the boy, who moves away at a speed of 1.0 m/s. The girl's speed is

Accepted Answer

We can solve this problem using the principle of conservation of momentum:

Initial momentum = Final momentum

The initial momentum is zero because both the girl and the boy are at rest. The final momentum is the sum of the momenta of the girl and the boy after the girl pushes the boy.

Final momentum = (mass of girl)(velocity of girl) + (mass of boy)(velocity of boy)
Final momentum = (30 kg)(v) + (25 kg)(1.0 m/s)

Since the initial and final momentum are equal, we can set them equal to each other:

0 = (30 kg)(v) + (25 kg)(1.0 m/s)

Solving for v, we get:

v = - (25 kg)(1.0 m/s) / (30 kg)
v = - 0.83 m/s

The negative sign indicates that the girl is moving in the opposite direction to the boy. Taking the absolute value, we get:

v = 0.83 m/s

Therefore, the girl's speed is 0.83 m/s, which is choice C.

Question 8

A piece of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball that is initially at rest. After the putty sticks to the ball, both move with a combined momentum of

Accepted Answer

The law of conservation of momentum states that the total momentum of a closed system is constant if no external forces act on it. Since the putty and the bowling ball stick together and no external forces are mentioned, their combined momentum after the collision is the same as the initial momentum of the putty, which is 1 unit.

Question 9

A rifle of mass 2 kg is suspended by strings. The rifle fires a bullet of mass 1/100 kg at a speed of 200 m/s. The recoil velocity of the rifle is about

Accepted Answer

The recoil velocity of the rifle can be calculated using the principle of conservation of momentum. Before firing, the total momentum of the system (rifle + bullet) is zero because neither is moving. After firing, the momentum of the bullet is its mass times its velocity, (1/100 kg) * (200 m/s) = 2 kg*m/s. For momentum to be conserved, the momentum of the rifle must be equal and opposite to this, so -2 kg*m/s. The mass of the rifle is 2 kg, so its velocity must be -2 kg*m/s divided by 2 kg, which equals -1 m/s. The negative sign indicates direction, so the magnitude of the recoil velocity is 1 m/s.

Question 10

A karate expert executes a swift blow and severs a cement block in two with her bare hand. The magnitude is the same for the

Accepted Answer

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. This means that the impulse (which is the product of force and the time over which the force is applied) is the same for both the karate expert's hand and the cement block. Therefore, the magnitude of the force, the time of impact, and consequently the impulse, are the same for both the block and the expert's hand.

Question 11

Consider driving into a massive concrete wall with no "give," versus having a head-on collision at the same speed with an identical car moving toward you at the same speed. It would be more damaging to hit the

Accepted Answer

The damage to your car would be roughly the same in both scenarios because the relative speed and impact force are similar in both cases. Hitting a massive concrete wall with no "give" or an identical car head-on at the same speed essentially results in the same amount of energy needing to be absorbed by the cars involved in the crash.

Question 12

If an astronaut whose total mass is 100 kg ejects 0.1 kg of gas at a speed of 50 m/s from her propulsion pistol, her recoil speed is

Accepted Answer

Using the conservation of momentum, the recoil speed can be calculated as (0.1 kg * 50 m/s) / 100 kg = 0.05 m/s.

Question 13

A 1-kg chunk of putty moving at 1 m/s collides and sticks to a 5-kg bowling ball initially at rest. The bowling ball and putty then move with a momentum of

Accepted Answer

The total momentum before the collision is the sum of the momentums of the putty and the bowling ball. Since the bowling ball is initially at rest, its momentum is 0. The momentum of the putty is its mass times its velocity, which is $1\, \text{kg} \times 1\, \text{m/s} = 1\, \text{kg} \cdot \text{m/s}$. By the conservation of momentum, the total momentum after the collision is the same as before the collision, which is $1\, \text{kg} \cdot \text{m/s}$.

Question 14

A ball is moving at 4 m/s and has a momentum of 48 kg ∙ m/s. What is the ball's mass?

Accepted Answer

The momentum of an object is defined as the product of its mass and velocity. Therefore, we can use the formula p = mv to solve for the mass of the ball.

p = mv
48 kg · m/s = m · 4 m/s
Dividing both sides by 4 m/s gives: 
12 kg = m

Therefore, the mass of the ball is 12 kg, and the best choice is B.

Question 15

A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish swimming toward it at 4 m/s. The speed of the larger fish after lunch is

Accepted Answer

The answer of A 5-kg fish swimming at a speed...

Question 16

Two billiard balls having the same mass roll toward each other, each moving at the same speed. What is the combined momentum of the two balls?

Accepted Answer

Momentum is a vector quantity, meaning it has both magnitude and direction. When two objects of equal mass move towards each other at the same speed and collide, their momenta are equal in magnitude but opposite in direction. Therefore, they cancel each other out, resulting in a combined momentum of 0 kg∙m/s.

Question 17

A 5.0-kg blob of clay moving at 2.0 m/s slams into a 4.0-kg blob of clay at rest. The speed of the two blobs stuck together after colliding is about

Accepted Answer

The answer of A 5.0-kg blob of clay moving at...

Question 18

A 1-N apple falls to the ground. The apple hits the ground with an impact force of about

Accepted Answer

The impact force of the apple hitting the ground cannot be determined with the information given. Factors such as the height from which the apple falls, the time it takes to stop upon hitting the ground, and the material properties of the ground and apple are necessary to calculate the impact force.

Question 19

Compared with the force that brings a small car to a stop, the force required to bring a heavy truck traveling at the same speed to a stop

Accepted Answer

The answer of Compared with the force that brings a...

Question 20

A cannonball shot from a cannon with a long barrel will have a greater muzzle velocity because the cannonball receives a greater

Accepted Answer

A longer barrel allows the force to act over a longer time, increasing the impulse, which results in a greater change in momentum and thus a higher muzzle velocity.

Quiz 4: Momentum and Energy