A jogger is moving at 5 m/s as she approaches a busy street. She needs to stop in 2 seconds in order to stay safe. What average deceleration must she have in order to stop in time?

Answer 1

using the kinematic equation: Vf = Vo + at
Vf = final velocity = 0m/s because she comes to a stop
Vo = initial velocity = 5m/s as she is jogging
a = acceleration (or in this case deceleration)
t = time elapsed = 2 s
so...
Vf = Vo + at
0m/s = 5m/s + a * 2s
-5m/s = a * 2s
(-5m/s)/2s = a
-2.5 m/s^2 = a
because the acceleration ends up being negative it is understood to be deceleration.

Answer 2

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