Question 1

Neglecting air resistance, a man on a high ladder releases a ball which strikes the ground with 100 J of kinetic energy. If he were to throw it straight upward instead, it will eventually reach the ground with a kinetic energy of

Accepted Answer

The kinetic energy when the ball hits the ground is solely dependent on the height from which it was released or thrown, not the direction of the throw. Neglecting air resistance, energy conservation ensures that the ball will have the same kinetic energy upon reaching the ground, regardless of whether it was dropped or thrown upwards.

Question 2

A heavy and a light object released from the same height in a vacuum have equal

Accepted Answer

In a vacuum, the absence of air resistance means that all objects, regardless of their mass, will experience the same acceleration due to gravity. This is a direct consequence of Newton's second law of motion and the universality of free fall.

Question 3

A feather and a coin dropped in a vacuum fall with equal

Accepted Answer

In a vacuum, there is no air resistance, so all objects, regardless of their mass, fall with the same acceleration due to gravity. This is a direct consequence of Galileo's principle of falling bodies and Newton's second law of motion.

Question 4

An object lifted 10 meters gains 200 J of potential energy. If the same object is lifted 20 meters, its potential energy gain is

Accepted Answer

Potential energy is directly proportional to height. Doubling the height from 10 meters to 20 meters doubles the potential energy from 200 J to 400 J.

Question 5

Two identical freight cars roll without friction (one at 1 m/s, the other at 2 m/s) toward one another on a level track. They collide, couple together, and roll away in the direction that

Accepted Answer

The direction after the collision depends on the momentum of the cars. Since both cars are identical but one has a higher velocity (2 m/s), it has more momentum. Therefore, after colliding and coupling together, they will move in the direction of the faster car, as it contributes more to the total momentum of the system.

Question 6

A jack system will increase the potential energy of a heavy load by 1000 J with a work input of 2000 J. The efficiency of the jack system is

Accepted Answer

The efficiency of the jack system is calculated as the output energy (potential energy increase of the load) divided by the input energy (work done), then multiplied by 100 to get a percentage. Therefore, efficiency = (1000 J / 2000 J) * 100 = 50%.

Question 7

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. The force depends on the duration of the impact and the distance over which the apple is stopped, neither of which are provided.

Question 8

A golf ball moving forward with 1 unit of momentum strikes and bounces backward off a heavy bowling ball that is initially at rest and free to move. The bowling ball is set in motion with a momentum of

Accepted Answer

Due to the conservation of momentum, the total momentum before and after the collision must be equal. Since the golf ball bounces backward, it must have reversed its momentum, meaning the bowling ball must have gained more than 1 unit of momentum to conserve the total momentum of the system.

Question 9

Two identical arrows, one with twice the kinetic energy of the other, are fired into a hay bale. The faster arrow will penetrate

Accepted Answer

The penetration distance is proportional to the kinetic energy. If one arrow has twice the kinetic energy, it will penetrate twice as far as the slower arrow.

Question 10

Momentum is transferred to the ground when an apple falls on it. The momentum absorbed by the ground is

Accepted Answer

The answer of Momentum is transferred to the ground when...

Question 11

When a rifle is fired it recoils as the bullet is set in motion. The rifle and bullet ideally acquire equal

Accepted Answer

According to the law of conservation of momentum, the total momentum of a system remains constant if no external forces act on it. Therefore, in the case of a rifle firing a bullet, the rifle and bullet system must have zero total momentum before and after the shot. This means that if the bullet acquires some momentum in the forward direction, the rifle must acquire an equal amount of momentum in the backward (or opposite) direction. Therefore, the correct answer is A), but opposite amounts of momentum. Option B) is incorrect because kinetic energy is not necessarily conserved in the system.

Question 12

It takes 40 J to push a large box 4 m across a floor. Assuming the push is in the same direction as the move, what is the magnitude of the force on the box?

Accepted Answer

The work done on an object is calculated by the formula Work = Force × Distance. Given that the work done is 40 J and the distance is 4 m, we can rearrange the formula to solve for force: Force = Work / Distance = 40 J / 4 m = 10 N.

Question 13

A 5000-kg freight car moving at 2 m/s runs into a 10,000-kg freight car at rest. They couple upon collision and move away as one body at

Accepted Answer

The answer of A 5000-kg freight car moving at 2...

Question 14

The impulse-momentum relationship is a direct result of

Accepted Answer

The impulse-momentum relationship is directly derived from Newton's 2nd law of motion, which states that the force acting on an object is equal to the rate of change of its momentum. This relationship is expressed as Impulse = Change in Momentum.

Question 15

Two identical arrows, one with twice the speed of the other, are fired into a hay bale. The faster arrow will penetrate

Accepted Answer

The penetration depth of an arrow (or any projectile) into a target is proportional to the square of its velocity. Therefore, if one arrow is moving at twice the speed of the other, it will penetrate four times as far, according to the kinetic energy formula (Kinetic energy = 1/2 mv^2, where m is mass and v is velocity).

Question 16

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

Accepted Answer

When bullets are fired from an airplane in the forward direction, the airplane experiences a backward reaction force (according to Newton's third law of motion), which results in a decrease in its forward momentum.

Question 17

If you push an object a given distance, while applying twice the force, you do

Accepted Answer

Work is defined as force times distance (W = F*d). If you double the force while the distance remains constant, the work done is doubled.

Quiz 5: Momentum and Energy