Question 1

A 5000-kg freight car crashes into a 10,000-kg freight car at rest. They couple upon collision and move with a speed of 2 m/s. What was the initial speed of the 5000-kg freight car?

Accepted Answer

The answer of A 5000-kg freight car crashes into 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

You're driving down the highway and a lovebug spatters onto your windshield. Which undergoes the greater force of impact?

Accepted Answer

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Therefore, the force of impact is the same on both the lovebug and the car.

Question 4

Suppose a gun were made of strong lightweight material with a pellet that is more massive than the gun. Then firing speed is greater for the

Accepted Answer

According to Newton's third law, when the gun fires, it will recoil backward with a force equal in magnitude but opposite in direction to the force exerted on the pellet. Since the pellet has more mass than the gun, it will have less acceleration than the recoil of the gun. Therefore, the recoil of the gun will be faster than the pellet.

Question 5

When a cannon fires a cannonball at a given speed, the smaller recoil speed of the cannon is due to different

Accepted Answer

According to Newton's Third Law, for every action, there is an equal and opposite reaction. When a cannon fires a cannonball, the cannonball exerts a force on the cannon, and the cannon exerts an equal and opposite force on the cannonball. The force on the cannonball causes it to accelerate and move forward, while the force on the cannon causes it to accelerate and move backward, which is the recoil. The momentum of the cannonball and the cannon must be conserved in this process. Since the cannonball has a much smaller mass than the cannon, the cannon experiences a much smaller change in velocity and, therefore, a smaller recoil speed. Thus, the mass of the cannon and the cannonball plays a crucial role in determining the recoil speed of the cannon.

Question 6

Recoil is noticeable if we throw a heavy ball while standing on a skateboard. If instead we go through the throwing motion but hold onto the ball, without friction effects our net recoil will be

Accepted Answer

According to the law of conservation of momentum, the momentum of the ball and skateboard system before and after the throwing motion should be the same. When we throw the heavy ball while standing on a skateboard, the momentum of the ball and skateboard system changes, resulting in a recoil. However, if we hold onto the ball and don't let it go, the momentum of the ball and skateboard system won't change. Therefore, there won't be any net recoil.

Question 7

The speed of a bullet fired from a gun will be about the same as the speed of the recoiling gun

Accepted Answer

The answer of The speed of a bullet fired from...

Question 8

When bullets are fired from an airplane in the forward direction of motion, the momentum of the airplane

Accepted Answer

When bullets are fired forward, they carry momentum in the forward direction. By conservation of momentum, the airplane must gain an equal amount of momentum in the opposite direction, causing its forward momentum to decrease.

Question 9

You're driving down the highway and a lovebug spatters onto your windshield. Which undergoes the greater change in momentum?

Accepted Answer

According to the law of conservation of momentum, the change in momentum experienced by the lovebug and the car is equal and opposite, so both undergo the same change in momentum.

Question 10

A sandbag is motionless in outer space. A second sandbag with 3 times the mass moving at 12 m/s collides with it and they both stick together and move at a speed of

Accepted Answer

The answer of A sandbag is motionless in outer space....

Question 11

Two identical freight cars roll without friction towards each other on a level track. One car rolls at 2 m/s and the other car rolls at 1 m/s. After the cars collide, they couple and roll together with a speed of

Accepted Answer

The answer of Two identical freight cars roll without friction...

Question 12

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

The impulse-momentum equation Ft = change in mv states that the force (F) exerted on an object for a period of time (t) will result in a change in momentum (change in mv). In this case, the momentum being reduced is that of the bungee jumper, who has a mass of m and is falling at a speed of v. Therefore, v in the equation refers to the speed of the jumper. The bungee cord itself does not have momentum in this situation, as it is not in motion.

Question 13

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

In both scenarios, the relative speed of impact is the same, resulting in the same amount of energy being dissipated. Therefore, the damage would be the same.

Question 14

A 1000-kg car moving at 10 m/s that brakes to a stop in 5 s has an average braking force of

Accepted Answer

The average braking force can be calculated using the formula: Force = (mass * change in velocity) / time. Here, the mass is 1000 kg, the change in velocity is 10 m/s (from 10 m/s to 0 m/s), and the time is 5 s. So, Force = (1000 kg * 10 m/s) / 5 s = 2000 N.

Question 15

You're driving down the highway and a lovebug spatters onto your windshield. Which undergoes the greater impulse?

Accepted Answer

Impulse is equal to the change in momentum, and according to Newton's third law, the force exerted by the lovebug on the car is equal and opposite to the force exerted by the car on the lovebug. Therefore, both the lovebug and the car experience the same impulse.

Question 16

A boxer punches a sheet of paper in midair from rest to a speed of 40 m/s in 0.05 s. If the mass of the paper is 0.01 kg, the force of the punch on the paper is

Accepted Answer

The answer of A boxer punches a sheet of paper...

Question 17

A karate expert executes a swift blow and severs a brick with her bare hand. Equal magnitudes occur for the

Accepted Answer

According to Newton's third law, the force applied by the expert's hand on the brick is equal in magnitude and opposite in direction to the force applied by the brick on the expert's hand. This means the impulse experienced by the brick and the hand is equal in magnitude as well. Also, since the brick and the hand are in contact for the same duration of time, the time of contact is equal for both. Therefore, all of the above choices are correct.

Question 18

The conservation of momentum is closely related to

Accepted Answer

The conservation of momentum is closely related to Newton's third law, which states that for every action, there is an equal and opposite reaction. When two objects interact, the force that each exerts on the other is equal and opposite, so the momentum of the system is conserved. This can be expressed mathematically as the sum of the momenta before the interaction is equal to the sum of the momenta after the interaction.

Question 19

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 with the force to stop the car, the force needed to stop the truck is

Accepted Answer

The force needed to stop an object is related to its momentum, which is the product of its mass and velocity. Since the truck has a greater mass than the car, it has more momentum at the same speed, requiring a greater force to stop it in the same amount of time.

Question 20

Compared with falling on a wooden floor, a wine glass may not break when it falls on a carpeted floor because of

Accepted Answer

A carpeted floor increases the time over which the wine glass comes to a stop, reducing the force experienced by the glass and thus decreasing the likelihood of breaking.

Quiz 3: Momentum and Energy