Ch6Momentum

Quiz.

1. Momentum is (Circle all that apply.)

a)inertia in motion

b)force times distance

c)force times time

d)mass times velocity

2. Impulse is (Circle all that apply.)

a)the change in momentum

b)force times time

c)speed times distance

3. When you have the same momentum at the end as you had in the beginning, that's called _____.

a)conservation of energy

b)conservation of momentum

c)conservation of force

4. An object that bounces has _____ impulse than an object that falls without bouncing.

a)less

b)the same

c)greater

d)not enough information to answer

5. Why can't you move your car by sitting in the driver's seat and pushing on the dashboard?

a)the car weighs too much

b)you would have to push for a really long time

c)the impulse must be caused by an external force

d)all of the above

6. Two objects with the same momentum may have different velocities.

a)True

b)False

7. One way to minimize the effect of force is to

a)reduce the time of impact

b)increase the amount of force

c)increase the time of impact

8. Leaning INTO a punch can reduce the impulse by shortening the time of impact.

a)True, even though it increases the force

b)False, it only increases the force

c)False, only increasing the time of impact can reduce the impulse

9. Momentum is a _____, therefore it _____ be negative.

a)scalar, cannot

b)vector, cannot

c)scalar, can

d)vector, can

Answer Key.

1. a) & d)

Momentum is given by the equation p=mv, but since mass is a measure of inertia and because only objects that are moving can have momentum, conceptually you would say that momentum is inertia in motion.

2. a) & b)

We derived in class from Newton’s second law and from the definition of acceleration that impulse is both the change in momentum and force times time.

3.b)

This should be self-explanatory.

4. c)

We also derived in class that the change in velocity is greater when an object bounces because velocity is a vector, so we must take the change in the object’s direction into consideration.

5.c)

When you are inside your car you are internal to its system, therefore you can never accelerate it without a net external force. You could, however, “Flintstone” it if you cut holes in the floorboard.

6.a)

The two objects would simply need to have different masses.

7.c)

The same amount of impact is imparted on a small force over a long time as a large force over a small time. This is the concept behind airbags.

8.a)

This is true, although what would be the point?

9.d)

The mathematical sign of a vector indicates direction in reference to a predetermined frame of reference