Most of the energy will be absorbed by the materials that make up the cars, causing them to deform. The energy will also be converted into sound energy, causing a loud bang upon collision. Also, some energy will be converted to thermal energy, which will cause the cars to heat up slightly.
Power is defined as the rate at which the body is doing work:

Work is defined as displacement done by the force times that displacement:

We know that we need 62N to move the box, so when we apply this force along the path of 10m we have done:

of work.
Now we just divide that by 5s to get how much power is required:
The car at 60 kph has 9 times more kinetic energy than the car traveling at 20 kph. This assumes that both cars have the same mass. Kinetic energy depends on the square of thee speed so if one car is going 3 times faster, its kinetic energy will be 3^2 ( = 9 ) greater. The car going at 60 kph will have 4 times the KE of the car going at 30 kph ( again assuming that the cars have the same mass.)
That is called pseudoscience
About 10% to 15% of system charge