Question

A car of mass 480 kg moving at a speed of 54 km $h^{-1}$ is stopped by applying brakes in 10 s. Calculte 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 =$\frac{(v–u)}{t}$
Or, a =$\frac{(0–15)}{10}=-1.5\frac{m}{s^2}$
Here, negative sign indicates retardation.
Now, Force = Mass x Acceleration
Or, F = $(480\times 1.5)=720N$