Question

a motorcar is moving with the velocity of 108km/h and it takes 4 second to stop after brake applied calculate the force exerted by the brake on the motor car if it's mass is 1000kg

Answer 1

108 km/h = 30m/s
when the car stops velocity of the car will b 0
using ' v = u - at ' ( v = final & u = initial velocity , a = deceleration, t = time)
we get a = 7.5 ms⁻² 
mass of the car = 1000kg
so force exerted by the brakes on themotorcar
= 1000 × 7.5 = 750 N

Answer 2

initial velocity, u = 108kmph = 108*5/18 = 30 m/s
final velocity, v = 0
Time to stop, t = 4sec
Acceleration = a

V = u + at
0 = 30 - a*4
a = 30/4 = 7.5m/s^2

Force exerted by the brake on the motor car = m*a = 1000*7.5 = 7500N