Question

A car of mass 480 kg moving at a speed of 54 km h^-1 is stopped by applying brakes in 10 s . Calculate the force applied by the brakes . 

Answer 1

Mass, m = 480 kg.

Initial velocity, u = 54 km/hr = 15 m/s.

Final velocity, v = 0.

Time, t = 10 s.

Acceleration = Change in velocity/time.

Or, a = (v - u)/t.

Or, a = (0 - 15)/10 = -1.5 ms^-2.

Here, negative sign indicates retardation.

Now, Force = Mass × Acceleration

Or, F = (480) (1.5) = 720 N.