I am not sure which equations I should use for each part. A 7550kg rocket blasts

Question

I am not sure which equations I should use for each part.

A 7550kg rocket blasts off vertically from the launch pad with a constant upward acceleration of 2.15m/s2 and feels no appreciable air resistance. When it has reached a height of 590m , its engines suddenly fail so that the only force acting on it is now gravity. What is the maximum height this rocket will reach above the launch pad? How much time after engine failure will elapse before the rocket comes crashing down to the launch pad? How fast will it be moving just before it crashes?

Explanation / Answer

Part A)

Start by finding the velocity at the end of the acceleration

Apply vf^2 = vo^2 + 2ad

vf^2 = 0 + 2(2.15)(590)

vf = 50.4 m/s

Then, gravity acts on it from there

vf^2 = vo^2 + 2ad

0 = (50.4)^2 + (2)(-9.8)(d)

d = 129 m

Add the two distances

129 + 590 = 719 m

Part B)
How much time to get to the top of the path from the engine shut off...

vf = vo + at

0 = 50.4 + (-9.8)(t)

t = 5.14 sec

How much time to fall from 719 m

d = vot + .5at^2

719 = 0 + (.5)(9.8)(t^2)

t = 12.11 sec

Add the two times

12.11 + 5.14 = 17.25 sec

Part C)
vf = vo + at

vf = (0) + (9.8)(12.11)

vf = 118.7 m/s (Your answer key may want this answer as negative since the velovity is downward.)

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