# Linear Momentum - Checking quick questions

What is the SI unit of momentum? --> N x s

When a light beach ball rolling with a speed of 6.0 m/s collides with a heavy exercise ball at rest, the beach ball's speed after the collision will be, approximately? --> 6.0 m/s

In an inelastic collision, if momentum is conserved, then which of the following statements is true about kinetic energy? --> Kinetic energy is lost.

Which of the following is an accurate statement?
The momentum of a projectile is constant. <---
The momentum of a moving object is constant.
If an object is acted on by a non-zero net external force, its momentum will not remain constant.
If the kinetic energy of an object is doubled, its momentum will also be doubled.

A 4.0 N force acts for 3.0 s on an object. The force suddenly increases to 15N and acts for one more second. What impulse was imparted by these forces on the object? --> 16.3 N·s

Thanks!

## Answers and Replies

I can't figure out how to find the impulse without mass...

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1 and 2 are correct.

For #3, the answer is a bit ambiguous. All KE need not be lost.

#4 - Wrong. Hint: Newton's 1st law.

#5 - How did you get 19? What's the definition of impulse?

For #3:
If an object is acted on by a non-zero net external force, its momentum will not remain constant.
This seems to comply with the 1st law.

Impulse is what changes the momentum of an object.. right?

Don't worry about it, I'll ask the teacher.

Thanks!

For #3:
If an object is acted on by a non-zero net external force, its momentum will not remain constant.
This seems to comply with the 1st law.
Right. So is a projectile free of non-zero net external forces?

Impulse is what changes the momentum of an object.. right?
Well, not exactly. Force is what changes momentum. Impulse is change in momentum(in a certain time interval).

$$J = F\Delta t = \Delta p$$, for a constant force F. J is impulse, btw.

Don't worry about it, I'll ask the teacher.

Thanks!

Now you tell me! :grumpy: i just cant comprehend getting the impulse without mass.