The car is moving at a speed of 40 m / s. With what speed should it move so that its kinetic energy is reduced by 4 times?

Given:

v = 40 meters per second – vehicle speed;

E1 is the kinetic energy of the vehicle;

E1 / E2 = 4 – the kinetic energy of the car decreased by 4 times.

It is required to determine the vehicle speed v2 (m / s).

Let m be the mass of the car. Then, the kinetic energy in the first case will be equal to:

E1 = m * v ^ 2/2, and in the second case: E2 = m * v2 ^ 2/2.

E1 / E2 = 4;

(m * v ^ 2/2) / (m * v2 ^ 2/2) = 4;

v ^ 2 / v2 ^ 2 = 4;

v / v2 = 2;

v2 = v / 2 = 40/2 = 20 m / s.

Answer: for the kinetic energy to decrease by 4 times, the vehicle speed must be 20 m / s.