## SAT Physics Subject Test

## Chapter 5 Linear Momentum

### Chapter 5 Review Questions

See __Chapter 17__ for solutions.

__1__. An object of mass 2 kg has a linear momentum of magnitude 6 kg • m/s. What is this object”s kinetic energy?

(A) 3 J

(B) 6 J

(C) 9 J

(D) 12 J

(E) 18 J

__2__. A ball of mass 0.5 kg, initially at rest, acquires a speed of 4 m/s immediately after being kicked by a force of strength 20 N. For how long did this force act on the ball?

(A) 0.01 s

(B) 0.02 s

(C) 0.1 s

(D) 0.2 s

(E) 1 s

__3__. A box with a mass of 2 kg accelerates in a straight line from 4 m/s to 8 m/s due to the application of a force whose duration is 0.5 s. Find the average strength of this force.

(A) 2 N

(B) 4 N

(C) 8 N

(D) 12 N

(E) 16 N

__4__. A ball of mass *m* traveling horizontally with velocity *v* strikes a massive vertical wall and rebounds back along its original direction with no change in speed. What is the magnitude of the impulse delivered by the wall to the ball?

(A) 0

(B) *mv*

(C) *mv*

(D) 2*mv*

(E) 4*mv*

__5__. Two objects, one of mass 3 kg and moving with a speed of 2 m/s and the other of mass 5 kg and speed 2 m/s, move toward each other and collide head-on. If the collision is perfectly inelastic, find the speed of the objects after the collision.

(A) 0.25 m/s

(B) 0.5 m/s

(C) 0.75 m/s

(D) 1 m/s

(E) 2 m/s

__6__. Object #1 moves toward object #2, whose mass is twice that of object #1 and which is initially at rest. After their impact, the objects lock together and move with what fraction of object #1”s initial kinetic energy?

(A)

(B)

(C)

(D)

(E) None of the above

__7__. Two objects move toward each other, collide, and separate. If there was no net external force acting on the objects, but some kinetic energy was lost, then

(A) the collision was elastic and total linear momentum was conserved

(B) the collision was elastic and total linear momentum was not conserved

(C) the collision was not elastic and total linear momentum was conserved

(D) the collision was not elastic and total linear momentum was not conserved

(E) None of the above

__8__. A wooden block of mass *M* is moving at speed *V* in a straight line.

How fast would the bullet of mass *m* need to travel to stop the block (assuming that the bullet became embedded inside)?

(A) *mV*/(*m* + *M*)

(B) *MV*/(*m* + *M*)

(C) *mV*/*M*

(D) *MV*/*m*

(E) (*m* + *M*)*V*/*m*

__9__. Which of the following best describes a perfectly inelastic collision free of external forces?

(A) Total linear momentum is never conserved.

(B) Total linear momentum is sometimes (but not always) conserved.

(C) Kinetic energy is never conserved.

(D) Kinetic energy is sometimes (but not always)conserved.

(E) Kinetic energy is always conserved.

**Keywords**

isolated system

linear momentum

impulse

impulse-momentum theorem

law of conservation of linear momentum

collisions

elastic

inelastic

perfectly (completely, totally) inelastic

**Summary**

· Linear momentum is the product of mass and velocity, and is symbolized by **p**. Use the formula **p** = *m***v**.

· Impulse is the product of the average force and the time during which it acts. This force occurs only briefly and equals the object”s change in momentum.

· Conservation of linear momentum states that when two objects interact in an isolated system, the total linear momentum of the system will remain constant.

· Collisions of objects are classified as elastic or inelastic. Elastic collisions conserve kinetic energy. After an inelastic collision, the total kinetic energy is different from what it was before the collision.

· A perfectly inelastic collision is where the objects stick and move together.