# Homework Help: Velocity / Momentum Questions

1. Sep 7, 2007

### eraemia

1. The problem statement, all variables and given/known data

I have three questions:

1. "The car rounded the corner at a constant velocity." Would this statement make sense to a physicist?

2. A cup sitting on a table constantly receives upward momentum from the table, T or F?

3. Imagine that a 1.0 kg cart traveling rightward at 1.0 m/s hits a 3.0 kg cart at rest. Afterward, the smaller cart is observed to move leftward with a speed of 0.75 m/s. What impulse did the collision give the smaller cart at the expense of the larger?

2. Relevant equations

None

3. The attempt at a solution

1. No, the word velocity is being used incorrectly.
2. I don't know about this one. I would say true, if the compression contact interaction of the table can be considered as velocity (which is a component of momentum). False, if the table is not displacing anything, hence there is no displacement over time or velocity.
3. I don't understand the question. The collision gave the smaller car an impulse? Well, I suppose 0.75 kg m/s leftward? Or was there none?

2. Sep 7, 2007

### mgb_phys

1, correct
2, No momentum and force are quite different.
3, Impulse is force * time so has units of Newton seconds ( or kg m/s )
I don't see how part 3 can be true, the initial carts has ke = 0.5 * 1 * 1^2 = 0.5J
the second cart has ke = 0.5 * 3* 0.75^2 = 0.84J unless I have made a msitake in arithmetic.

3. Sep 7, 2007

### learningphysics

For part 3, impulse given to the small cart is change in momentum of the small cart... so the final momentum of the small cart - initial momentum of the small cart is what you need... careful about directions and signs.