# Homework Help: Acceleration and Free Fall Problem

1. Nov 10, 2009

### cheerspens

1. The problem statement, all variables and given/known data
A rocket is fired vertically and ascends with a constant vertical acceleration of 20.0 m/s^2 for 2.00 seconds. Its fuel is then used up and it continues as a free object. What is the maximum altitude reached?

2. Relevant equations
X=Xo+Vot+(1/2)at^2
V=Vo+at
2a(X-Xo)=V^2-Vo^2

3. The attempt at a solution
I usually start off making an x vs. t, v vs. t, and an a vs. graph in order to get a variable list so I can plug into the equation and solve but I'm thrown off by how to even begin the problem when it says it runs out of fuel and continues as a free object.

2. Nov 10, 2009

### mgb_phys

At the end of the powered flight it becomes a free falling projectile (like a cannon ball in the normal questions) you just need to work out the starting velocity and height at the point the fuel runs out.

ps. Don't forget to add this start height to your answer for the free fall part of the flight.

3. Nov 10, 2009

### cheerspens

Is the height of the point the fuel runs out the maximum height reached?

4. Nov 10, 2009

### mgb_phys

No
Consider the point the fuel runs out. Then it is exactly the same as throwing/firing an object upwards with a certain speed from that point.

Then all the same 'a cannon ball is fired with a speed ....' questions you have probably already done - apply.

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