# Dynamics rocket car problem

1. Feb 17, 2013

### canucks81

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

A 1200 kg rocket car is placed at the bottom of a 100 meter long ramp inclined at 10°. The rocket is turned on and it exerts a force of 8300 N for 5.70 seconds, and then it shuts down. Find the speed with which the rocket car leaves the ramp (assume frictionless).

2. Relevant equations

http://img98.imageshack.us/img98/9425/54fl1.png [Broken]

3. The attempt at a solution

http://i.imgur.com/MGDp7Rf.png?1

I didn't show all of my solution but I need to know if that part is correct. What I did next is I assumed vi = 0 and the used the formula vf = vi + at which gave me an answer of 29.7 m/s, however, the correct answer is 28.8 m/s.

Last edited by a moderator: May 6, 2017
2. Feb 17, 2013

### haruspex

You've calculated the max speed. Did you use the ramp length?

3. Feb 17, 2013

### canucks81

What do I do with the ramp length? I didn't use it.

4. Feb 17, 2013

### haruspex

You're asked for the speed at the end of the ramp, not the speed when the engine shuts down.

5. Feb 17, 2013

### canucks81

So would I calculate the distance traveled up to when the engine shuts down, then subtract it from the length of the ramp to find the remaining distance?

6. Feb 17, 2013

### haruspex

That'll work.

7. Feb 17, 2013

### canucks81

I'm not sure how to get the new acceleration from when the engine shuts down. I know that it has to be negative because the rocket will slow down.