If a car goes five times as fast how much more kinetic energy will it have?

For that answer, we should take a second to look at the formula for kinetic energy:

                Kinetic Energy of an object = (mass) x (speed)² .

The important thing to notice is that the KE is proportional to the square of
the speed. So if you multiply the speed by some number, the KE changes
by the square of that number.

Multiplying the speed of the car by 5 gives it (5)² = 25 times as much KE.