Classes are canceled due to snow, so you take advantage of the extra time to con

Question

Classes are canceled due to snow, so you take advantage of the extra time to conduct some physics experiments. You fasten a large toy rocket to the back of a sled, and take the modified sled to a large, flat, snowy field. You ignite the rocket, and observe that the sled accelerates from rest in the forward direction at a rate of 15.5 m/s2 for a time period of 2.90 s. After this time period, the rocket engine abruptly shuts off, and the sled subsequently undergoes a constant backward acceleration due to friction of 4.15 m/s2. After the rocket turns off, how much time does it take for the sled to come to a stop?

Explanation / Answer

given, initial acceleration, a = 15.5 m/s/s
time taken for this acceleration t = 2.9 s

so final velocity after this time t, v = at = 15.5*2.9 = 44.95 m/s
after reaching this velocity it takes time t for the sled to stop
deceleration, d = 4.15 m/s/s

so, 0 = v - dt
t = v/d = 44.95/4.15 = 10.831 s
so the sled stops after 10.831 seconds

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