# Linear Momentum - Checking quick questions

1. Mar 16, 2007

### future_vet

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!

2. Mar 16, 2007

### future_vet

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

Last edited: Mar 16, 2007
3. Mar 16, 2007

### neutrino

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?

4. Mar 16, 2007

### future_vet

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.

5. Mar 16, 2007

### future_vet

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

6. Mar 16, 2007

### future_vet

Thanks!

7. Mar 16, 2007

### neutrino

Right. So is a projectile free of non-zero net external forces?

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.

8. Mar 16, 2007

### neutrino

Now you tell me! :grumpy:

9. Jan 19, 2011

### oriowo temito

i just cant comprehend getting the impulse without mass.