What is the rocket's initial upward acceleration?

[cookiekid20]

Homework Statement

A 20000kg rocket has a rocket motor that generates 3E5 N of thrust.
PartA:
What is the rocket's initial upward acceleration? Express your answer using two significant figures.
Part B:
At an altitude of 5km the rocket's acceleration has increased to 6m/s^2. What mass of fuel has it burned? Use wo significant figures in your answer.

Homework Equations

Part A:
I used the equation F_thrust_=ma-mg_earth_
Part B:
I dont' know the equation.

The Attempt at a Solution

PartA: I got the right answer 5.2 m/s^2
Part B: I got it wrong i tried using the same equation as part A but didn't work.

 

[Dick]

It should have worked. The thrust is constant only m has changed. What did you get?