Question

calculate the work required to stop the car of 1500kg moving at a speed of 72km/h by applying brakes.

Answer 1

Work done = change in kinetic energy 
final velocity = 0 m /s 
initial velocity = 72×5/18 = 20 m/s

$W = \frac{1}{2} m v^{2} - \frac{1}{2} mu^{2}$

1/2 ×1500 (0×0-20×20)
750×-400
=-300000 J

Answer 2

⇒Work done=Change in kinetic energy............ ⇒KE=1/2mv²....... ⇒Mass->15000kg........ ⇒Velocity->72km/h...... ⇒KE=1/2×15000×(72)²....... ⇒KE=1/2×15000×5184....... ⇒KE=7500×5184...... ⇒KE=3888×10×10³J........ So work require will be 3888×10×10³J.......!!