# Homework Help: Rocket Acceleration Problem

1. Feb 13, 2013

### revults

1. The problem statement, all variables and given/known data
A rock of blasts of vertically from rest on the launch pad with an upward acceleration 2.60 m/s^2= At 30s after blast off, the engine suddenly fails, which means the force they instantly stops.

2. Relevant equations

3. The attempt at a solution

How high above the launch pad will the rocket eventually go?

height = ½at² = ½•2.6m/s²•(30s)² = 1170 m

I keeping getting that answer, but the online system says its wrong.

Also I have no idea how to solve this.

Find the magnitude of the rocket's acceleration at its highest point.

Last edited: Feb 13, 2013
2. Feb 13, 2013

You are correct, that's the height at 30 seconds. If the engines fail at 30 seconds, does that mean the rocket stops there and begins to freefall?

For the second part, think about the velocity of the rocket at its highest point.

Alex

3. Feb 13, 2013

### revults

yeah the force they produce instantly stop

I rewrote the question in the way it was typed in my online assigment.

4. Feb 13, 2013

A good analogy is putting your foot on the brake in your car. When you brake, does the car instantaneously stop?

In this case, the rocket engine failing is "applying the brake" and gravity is "pushing the brake pedal".

This equation may help (rearrange the variables): vf = v0 + at

Alex

5. Feb 13, 2013

### fgb

Plotting the graph of speed x time and thinking about what is the meaning of the area in this graph might make the problem easier.

The speed x time graph usually comes in handy when you're dealing with mixed accelerations. :)