Question

A driver moving at a constant speed of 30m/s sees an accident up ahead and hits the
brakes. If the car decelerates at a constant rate of -5m/s2, How far does the car go before it
comes to stop ? A. 90m B. 100m C. 40m D. 20m

Answer 1

Use v_f^2 = v_i^2 + 2aΔx. With v_f = 0, v_i = 30 m/s, a = −5 m/s^2:

0 = 30^2 + 2(−5)Δx → 900 = 10Δx → Δx = 90 m.

Answer: A. 90 m.