Question

An auto driver moving with 36km/hr sees a child standing in the middle of the road. he applied breaks and bring s his vehicle to rest in 5 seconds to save the child. if the total mass of the auto and the driver is 450 kg, calculate the force of the brakes.

Answer 1

On converting 36 km/h to m/s, we get 10 m/s.
Time taken to come to 0m/s from 10m/s = 5s.
According to the equation
v = u + at,
0 = 10 - a×5 (minus sign because acceleration is negative)
On rearranging, we get
a = 2 m/s2.
Now, force(F) = mass(m) × acceleration(a)
Or,
F = ma;
Therefore,
F = 450kg × 2m/s2
= 900N