A car weighing 1.2 tons moving at a speed of 72 km / h began to brake and reached a full stop 100 m

A car weighing 1.2 tons moving at a speed of 72 km / h began to brake and reached a full stop 100 m, which is equal to the coefficient of friction.

Initial data: m (vehicle weight) = 1.2 t; V (speed before braking) = 72 km / h; S (path to a complete stop) = 100 m.

Constants: g = 10 m / s ^ 2.

SI system: m = 1.2 t = 1.2 * 1000 kg = 1200 kg; V = 72 km / h = 72 / 3.6 m / s = 20 m / s.

1) Determine the acceleration with which the car braked:

S = (V ^ 2 – V0 ^ 2) / 2a = (0 – V0 ^ 2) / 2a.

a = -V0 ^ 2 / 2S = -20 ^ 2 / (2 * 100) = -400 / 200 = -2 m / s ^ 2.

2) Find the coefficient of friction:

| m * a | = | Ftr. | = | μ * m * g |.

μ = m * a / (m * g) = a / g = 2/10 = 0.2.