# A car is heading 43 m/s east. Find momentum, velocity

1. Mar 6, 2014

### Medgirl314

A friend asked for help with a problem, and I tried to go about it as logically as possible. His class is different, so I wasn't really sure how far into it they were and what equations to use. Anyway, I wanted to make sure we didn't get it wrong. Could someone check it, please? I'm especially concerned that we never took direction into account, and that we weren't sure how to take the law of conservation of momentum into account.

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

A 1,988 kg car is moving at 43 m/s east. Suddenly, the driver slams on the brakes for 1.8 seconds, exerting a force of 6,000 N to the car.

A. What is the initial momentum of the car?

B. What is the change in momentum?

C. What is the final momentum of the car?

D. What is the final velocity of the car?

2. Relevant equations
a=f/m
v=v0+at
p=mv

3. The attempt at a solution

A. What is the initial momentum of the car?
p=mv
p=1988*43
p=85484 kg m/s

B. What is the change in momentum?
85484 kg m/s-74669 kg m/s=10815 kg m/s
C. What is the final momentum of the car?
p=1988*37.56 m/s
p=74669 kg m/s

D. What is the final velocity of the car?
a=f/m
a=6000/1988
a=-3.02 m/s^2
v=43+-3.02*1.8
v=37.56 m/s^2

2. Mar 6, 2014

### SammyS

Staff Emeritus
My guess is that it's intended for this question to be answered using impulse.

Apply the Impulse - Momentum Theorem.

The solution is fairly simple to obtain that way.

3. Mar 6, 2014

### Medgirl314

Wow, I can't believe how much I over-complicated that one. Oops. He said he re-worked it with the theorem and got the same answer.Thank you!!!

4. Mar 13, 2014

### Medgirl314

Could someone please confirm if this is the right answer? His physics teacher didn't provide a solution.

5. Mar 13, 2014

### SammyS

Staff Emeritus
What do you get using Impulse & Momentum ?