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.
