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Old Sep 7th 2009, 07:43 PM   #1
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Mastering Physics question

A 200 kg weather rocket is loaded with 100 kg of fuel and fired straight up. It accelerates upward at 33 m/s^2 for 32 seconds , then runs out of fuel. Ignore any air resistance effects.

a) what is the rocket's maximum altitude?
b) how long is the rocket in the air?

I think the part that confuses me is the mass, if you could help me with this question that would be greatly appreciated.
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Old Sep 7th 2009, 07:58 PM   #2
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Ignore the mass and continue the question like regular.
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Old Sep 26th 2009, 07:25 PM   #3
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How do you determine the acceleration for this question though?
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Old Sep 27th 2009, 03:04 AM   #4
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Solidsnake,

You have already asked a similar question to this on the 5/9/09 called Mastering Physics practice question.

I know this because i made a complete mess of it myself until physicsquest came along, i understand the equation now. (Thanks to physicsquest)

u=initial velocity
v=final velocity
t=time
a=acceleration
s=displacement

to find the altitude (s) you first need to find the velocity (v), v= u + at

u=0 , a=33m/s^2 , t=32, v=0+ 33 x 32 = 1056 m/s

displacement (s) after fuel runs out = v^2 = 0= u^2 - 2as (a= being gravity, 9.8)
1056^2 = 1115136 (take into account that v becomes u)
1115136-1115136 = v^2, (v^2 in this case will be 0)
1115136/(2a) = s
s= 56894.69 m, after fuel runs out

t = s/((u+v)/2)
t= 56894.69/((1056+0)/2) = 107.755 secs, after fuel runs out

I'll leave you to find the rest, you still need to find (t) & (s) when the rocket had fuel and like Deco stated mass is irrelevant if your given (a) & (t), so you only need to find (s).

Last edited by Paul46; Sep 27th 2009 at 07:56 AM. Reason: spelling
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