Question

a car is moving with the speed of 72 km/hour. because a child is crossing the road. then the driver brakes the car. at 10 seconds since braking, calculate the acceleration of the car if,
a. the speed of car becomes 18 km/jam
b. the car stops

Answer 1

Given,

Initial speed, u = 72 km/ hr =72×5/18 =20m / s

Time taken, t = 10 sec

(a) final speed, v = 18 km/ hr =18×5/18 =5 m/sec

acceleration, a = v-u/t = 5-20/10 = -15/10 = - 1.5m/s square

(b) v = 0

a = v-u/t = 0-20/10= -20/10= -2 m/sec square.