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February 28, 2015

February 28, 2015

Posted by **Lindsay** on Sunday, September 30, 2007 at 12:34pm.

a) What is the max. height reached by the rocket?

b) When does the rocket reach max. height?

c) How long is the rocket in the air?

I really need help with which equation to use for this problem. I'm unsure of even where to begin...!

- Physics -
**drwls**, Sunday, September 30, 2007 at 1:02pma) First, calculate the velocity Vmax attained during acceleration at rate a. (They already tell you the altitude there, H = 150 m). Then compute how huch higher it "coasts" before reaching maximum altitude.

Vmax = sqrt(2aH)= 24.5 m/s

To have the velocity decrease to zero, the additional time of flight t' is given by

g t' = 24.5 m/s, so

t' = 24.5/9.8 = 2.5 s

The average speed while coasting to zero velocity is Vmax/2 = 12.25 m/s.

Additionl altitude gained = (2.5)(12.25) = 30.63 m

Maximum altitude = Hmax = 150 + 30.63 = 180.63 m

b) it attains maximu height 2.5 seconds after accelerqation stopped. We already calculated that. Add that to the tiome spent accelerating for the total time after launch. The time t spent accelerating is given by

(1/2) a t^2 = 150 m

t = sqrt (2*150/a)= 12.25 s

Total time to reach maximum altitude - t + t' = ?

c) Add to the last answer the time that it takes to fall back down. Call this time t"

(1/2) g t"^2 = Hmax

Solve for t" and add it to the time in the previous answer

- Physics -
**Stephanie**, Sunday, September 30, 2007 at 2:45pmFor part a, my book says the answer is 310 m. I'm still really confused on how they got this answer.

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