Question

Find the force applied by car brakes knowing that the mass of the car is 3000 kg, velocity 20 m/s and that the brakes applied 55 meters before the stoplight

Answer 1

use the work-energy relation
\[ \frac{1}{2} m v^2 = F s \]
so we get
\[ F = \frac{1}{2}\frac{mv^2}{s} \]