A test rocket is fired straight up from rest with a net acceleration of 20.0 m/s2. After 4.00 seconds the motor turns off, but the rocket continues to coast upward with no appreciable air resistance. What maximum elevation does the rocket reach?
A) 487 m
B) 327 m
C) 320 m
D) 408 m
E) 160 m

Question

Quizplus · Accepted Answer

The rocket accelerates for 4 seconds, reaching a velocity of 80 m/s (v = at). It then coasts upward, reaching a maximum height when its velocity becomes zero. The height during acceleration is 160 m (s = 0.5 * a * t^2), and during coasting, it rises an additional 327 m (using v^2 = u^2 + 2as). Total height is 487 m.

A Test Rocket Is Fired Straight Up from Rest with a Net