Posted by **urgent answer needed** on Saturday, June 15, 2013 at 4:43am.

A rocket accelerates straight up from rest for 20 seconds with an acceleration of 8 m/s2. After 20 seconds the rocket motor shuts off and the rocket continues to coast upwards. How high does the rocket go in meters?

Details and assumptions

You may take the acceleration of gravity as −9.8 m/s2.

You may neglect air resistance.

- physics -
**MathMate**, Saturday, June 15, 2013 at 7:29am
Acceleration phase:

initial velocity, v0 = 0 m/s

final velocity, v1 = at = 8*20 = 160 m/s

distance, S = ut+(1/2)at² = 0 + (1/2)8(20²)

=(1/2)8(400)=1600 m

Free fall phase:

v0 = 160 m/s

acceleration,a = -9.8 m/s²

v0 = 160 m/s

v1 = 0

a = g =-9.8 m/s²

use

v1²-v0²=2aS

to solve for S, distance.

Add this to the 1600 m in the acceleration phase to get the maximum height.

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