A car was moving at a constant speed of 30 mile/hr. The driver tried to apply th

Question

A car was moving at a constant speed of 30 mile/hr. The driver tried to apply the brakes as soon as saw a deer crossing the road. However, it took 0.25 sec to start braking because of the reaction time. Assume the brakes were applied in a uniform manner and it took 3 sec to br4ing the car to a full stop. a. Draw velocity versus time graph for the car's motion. b. What was the acceleration of the car while the brakes are applied? c. How far did the car travel from the moment the driver saw the deer to the full stop. d. It the car was moving at the speed of 25 miles/hr, how far would the car travel before coming to the rest.

Explanation / Answer

a] The velocity vs time graph will be a horizontal line for t = 0 to t = 0.25s after which it will be a downwards line with negative slope [deceleration] from t= 0.25s to t = 3.25s.

b] u = 30 mi/hr = 13.4112 m/s

a = [v - u]/t = [0 - 13.4112]/3 = - 4.4704 m/s2

c] d = (13.4112 x 0.25) + (13.4112 x 3) - (1/2)(4.4704)(3)2 = 22.4184 m

d] Repeat the procedure as shown for u = 30 mi/hr but instead use u = 25 mi/hr.

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