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**"launch a weather rocket" prbm**

## Homework Statement

A 1000 kg weather rocket is launched straight up. The rocket motor provides a constant acceleration for 11 s, then the motor stops. The rocket altitude 15 s after launch is 4600 m. You can ignore any effects of air resistance.

a) Acc. of rocket during the first 11s

b) Its speed at 15s

**2. Equations**

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V(final)^2 = V(init.)^2 + 2AS

-> therefore S = V(final)^2 / (2A) when V(init.) = 0

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S(final) = S(init.) = V(init.)t + .5At^2

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## The Attempt at a Solution

V(@11s) = S(init.) + V(init.)t + .5At^2

= 0 + 0t + .5a(11)^2 = 60.5a

thus S(first 11s) = V(@11s)^2 / 2a as V(init.) = 0

= (60.5a)^2 / 2a = 1830.125a

S(total) = 4600 = S(first 11s) + V(@11s)(4) + .5(0)t^2

4600 = 1830.125a + 60.5a(15-11) + 0 = (1830.125 + 242)a = 2072.125a

therefore a = 2.21994

and the homework system returns wrong. i hope someone can point out where i went wrong. thanks!