Rocket's Max Altitude & Flight Time

[jelder]

A 200kg weather rocket is loaded with 100 kg of fuel and fired straight up. It accelerates upward at 31.0 {\rm m/s^2} for 35.0 s, then runs out of fuel. Ignore any air resistance effects.

I just don't know how to integrate the weight into the problem

known variables (hopefully they are correct this may be where I went wrong)
vi=0m/s
xi=0km
xf=?
a=31.0m/s^2
t=35.0s



What is the rocket's maximum altitude?



How long is the rocket in the air?

 

[hage567]

Why do you think you need to take the mass into account? I don't think that it's relevant to the question as it makes it much more complicated than just basic kinematics. Actually, the information in the question is set up so you don't have to worry about it.

Think about this question in two pieces: one piece is when the fuel is burning, and the other is after the fuel runs out.

How do you think you can find the height of the rocket at the point where the fuel just runs out?