Question

calculate the work required to be done to stop a car of 1500kg moving at a velocity of 60km/hr

Answer 1

Mass of car = 1500 Kg

Velocity (V) = 60 Km/hr

              = 60 x 1000/3600 m/s

              = 16.67 m/s

Work done = Change in kinetic energy

                 = 1/2 mv22 - 1/2 mv12

where, m= mass. v1 = Initial velocity, v2 = Final velocity                  

So, Work done = 1/2 x1500 {(0)2 - (16.67)2}

                       =  1/2 x1500 {0 + 277.89}

                      = 1/2 x1500 x 277.89

                      = 208417.5 J

                      = 208. 41 kJ

Answer 2

Work required to stop the car should be equal to the present energy of car

Work = Kinetic energy of car
= 0.5 m v^2
= 0.5 × 1500 kg × (60 × 5/18 m/s)^2
= 208 333.333 joules
= 208.33 kilojoules