Acar of mass 800 kg is moving at a speed of 2.2 m/s. a man pushes the car, increasing the speed to 2.6 m/s. how much work did the man do?

Before the push:

Kinetic energy = (1/2) (mass) (speed)²

                     =  (400 kg) (2.2 m/s)²

                     =     1,936 joules .

After the push: 

Kinetic energy = (1/2) (mass) (speed)²

                     =  (400 kg) (2.6 m/s)²

                     =     2,704 joules  .

The car gained (2,704 - 1,936) = 768 joules of kinetic energy.
If there was no help from the engine or a down-hill slope, then
that additional energy could only have come from the pushing man.

therefore, the efficiency is: