# Exam 5 Numbers 1-5 Physics 2016-2017

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• 1.

### When comparing the momentum of two moving objects, which of the following is correct?

• A.

The object with the higher velocity will have less momentum if the masses are equal.

• B.

The more massive object will have less momentum if its velocity is greater.

• C.

The less massive object will have less momentum if the velocities are the same.

• D.

The more massive object will have less momentum if the velocities are the same.

C. The less massive object will have less momentum if the velocities are the same.
Explanation
Momentum is the product of mass and velocity. Therefore, if the velocities are the same, the object with less mass will have less momentum. This is because mass is directly proportional to momentum, so a decrease in mass will result in a decrease in momentum.

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• 2.

### Two skaters stand facing each other. One skater’s mass is 60 kg, and the other’s mass is 72 kg. If the skaters push away from each other without spinning,

• A.

The lighter skater has less momentum.

• B.

Their momenta are equal but opposite.

• C.

Their total momentum doubles.

• D.

Their total momentum decreases.

B. Their momenta are equal but opposite.
Explanation
When the skaters push away from each other without spinning, the law of conservation of momentum states that the total momentum of the system remains constant. Since momentum is a vector quantity, it has both magnitude and direction. The magnitude of momentum is given by the product of mass and velocity, while the direction is determined by the direction of motion. In this case, the skaters have equal and opposite momenta because they have the same magnitude of momentum but are moving in opposite directions. Therefore, their momenta are equal but opposite.

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• 3.

### In a two-body collision,

• A.

Momentum is always conserved.

• B.

Kinetic energy is always conserved.

• C.

Neither momentum nor kinetic energy is conserved.

• D.

Both momentum and kinetic energy are always conserved.

A. Momentum is always conserved.
Explanation
In a two-body collision, momentum is always conserved. This means that the total momentum before the collision is equal to the total momentum after the collision. Momentum is a vector quantity, which means it has both magnitude and direction. In a collision, the total momentum of the system remains constant, even if the individual momenta of the bodies change. This conservation of momentum is a fundamental principle in physics and is applicable to various types of collisions, such as elastic and inelastic collisions. However, kinetic energy is not always conserved in a collision. It can be transferred between the bodies or converted into other forms of energy, such as heat or sound.

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• 4.

### A person sitting in a chair with wheels stands up, causing the chair to roll backward across the floor. The momentum of the chair

• A.

Was zero while stationary and increased when the person stood.

• B.

Was greatest while the person sat in the chair.

• C.

Remained the same.

• D.

Was zero when the person got out of the chair and increased while the person sat.

A. Was zero while stationary and increased when the person stood.
Explanation
When the person was sitting in the chair with wheels, the momentum of the chair was zero because it was not in motion. However, when the person stood up, they exerted a force on the chair, causing it to move backward. As a result, the momentum of the chair increased because momentum is directly proportional to the mass and velocity of an object. Therefore, the correct answer is that the momentum of the chair was zero while stationary and increased when the person stood.

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• 5.

### Two swimmers relax close together on air mattresses in a pool. One swimmer’s mass is 48 kg, and the other’s mass is 55 kg. If the swimmers push away from each other,

• A.

Their total momentum triples.

• B.

Their momenta are equal but opposite.

• C.

Their total momentum doubles.

• D.

Their total momentum decreases.

B. Their momenta are equal but opposite.
Explanation
When the swimmers push away from each other, according to the law of conservation of momentum, the total momentum of the system remains constant. Since momentum is a vector quantity, it has both magnitude and direction. The fact that the swimmers have equal but opposite momenta means that the magnitude of their momenta is the same, but they are moving in opposite directions. This ensures that the total momentum of the system remains unchanged.

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