A car moving at a speed of 36 km / h after turning off the engine traveled 20 m before stopping.

A car moving at a speed of 36 km / h after turning off the engine traveled 20 m before stopping. What is the drag coefficient?

Vehicle speed expressed in m / s:

v = 36 * 1000/3600 = 10 m / s.

Let m be the mass of the car, then its kinetic energy, before turning off the engine:

Eк = mv ^ 2/2.

The drag force F is equal to the drag coefficient k multiplied by the weight mg of the car:

F = kmg.

The work of this force on the path s, traversed to the stop:

A = Fs = kmgs.

According to the law of conservation of energy:

Eк = А, or

mv ^ 2/2 = kmgs, whence

k = v ^ 2 / (gs) = 10 ^ 2 / (9.8 * 20) = 0.51.

Answer: 0.51.