A test rocket is fired straight up from rest with a net acceleration of 20 m/s 2

Question

A test rocket is fired straight up from rest with a net acceleration of 20 m/s2. After 4 seconds the motor turns off, but the rocket continues to coast upward. What maximum elevation does the rocket reach? Select one: a. 327 m b. 408 m c. 487 m d. 160 m e. 320 m A test rocket is fired straight up from rest with a net acceleration of 20 m/s2. After 4 seconds the motor turns off, but the rocket continues to coast upward. What maximum elevation does the rocket reach? Select one: a. 327 m b. 408 m c. 487 m d. 160 m e. 320 m Select one: a. 327 m b. 408 m c. 487 m d. 160 m e. 320 m a. 327 m b. 408 m c. 487 m d. 160 m e. 320 m

Explanation / Answer

answer is c. 487 m

The rocket's motor cuts out at an altitude of 160 meters.
4^2 * 20 / 2 = 160

The rocket now has velocity of 80 m/s.
4 * 20 = 80

It then begins to decelerate at a rate of 9.8 m/s/s, and will reach it's maximum altitude 8.163 seconds later.
80 / 9.8 = 8.163

During this 8.163 second time interval the rocket will climb an additional 326.531meters.
8.163^2 * 9.8 / 2 = 326.531

...for a total height of 486.531 meters.

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