A 1000kg weather rocket is launched straight up. The rocket motor provides a con

Question

A 1000kg weather rocket is launched straight up. The rocket motor provides a constant acceleration for 16s, then the motor stops. The rocket altitude 20s after launch is 6800 m . You can ignore any effects of air resistance.

Part A

What was the rocket's acceleration during the first 16s?

Express your answer to two significant figures and include the appropriate units.

Part B

What is the rocket's speed as it passes through a cloud 6800 mabove the ground?

Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

a)

Distance travelled in 16 sec

s = ut + 1/2*at^2

s= 0 + 1/2*a*16^2

s = 128a

After 16 secs,

v = u + at

v = 16a

Hence,

s = ut+1/2at^2

s = 16a*4 + 1/2*-9.8*4^2

s = 64a - 78.4

Hence

6800 = 128a + 64a - 78.4

a = 35.825 m/s^2

b)

After 16 secs,

v = u + at

v = 16a

v = 16*35.825

v = 573.2 m/s

Now

v20 = u - 9.8*4

v20 = 573.2 -  9.8*4

v20 = 534 m/s

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