Question

A force is applied on a car of mass 1500kg,show that its speed increases from 54km/hr to 72km/hr.find the work done by the force on the car

Answer 1

Mass of car m = 1500 kg
Initial velocity = 54 km/h = 54 x 5/18 = 15 m/s
Final velocity = 72 km/h = 72 x 5/18 = 20 m/s 
(1 km/h = 1000 m/ (3600 s) = 5/18 m/s
Initial kinetic energy = ½ mv2
                              = ½ x 1500 x (15)2
                              = 168750 J
Increased kinetic energy = 1/2 mv2
                           = ½ x 1500 x (20)2
                           = 300000 J
Work done = Change in kinetic energy
                = 300000 - 168750
                = 131250 J
Hence the work done by the force on the car = 131250J