# Homework Help: Free fall acceleration of rocket

1. Sep 13, 2009

### rich1116

I thought I had the answer to this problem, but it doesn't match the book's answer. I can't figure out what I'm doing wrong. This is the problem:

A rocket is launched straight up with constant acceleration. 4 seconds after liftoff, a bolt falls off the rocket and hits the ground 6 seconds later. What was the rocket's acceleration?

First, I used the free fall acceleration of the bolt, -9.80m/s2 and 6 seconds that if fell for to find its position when it fell off the rocket, which I found to be 176.4m. This would also be the height of the rocket when the bolt fell of. Since the rocket travelled for 4 sec to reach this height, I used this height and time to find the acceleration of the rocket, 22.05m/s2.
The book answer however is 5.5 m/s2.
What am I doing wrong?

2. Sep 13, 2009

Hello rich.You took the initial velocity of the bolt to be zero.It is not zero it is the upward velocity that the rocket has at the instant the bolt drops.

3. Sep 13, 2009

### rich1116

then how do i find the initial velocity?

4. Sep 13, 2009

You can write it in symbol form.

5. Sep 13, 2009

### rich1116

i can but symbols won't due me any good. i need a definite numerical answer to the question. i know i can write a bunch of equations but i have no numbers to put into them

6. Sep 13, 2009