# A car weighing 50 kn, moving by inertia at a speed of 10, due to friction, stops in 20 seconds.

A car weighing 50 kn, moving by inertia at a speed of 10, due to friction, stops in 20 seconds. determine the value of the friction force.

Initial data: P (vehicle weight) = 50 kN = 50 * 10 ^ 3 N; V (vehicle speed before braking) = 10 m / s; t (braking time) = 20 s.

Reference data: g = 10 m / s ^ 2.

1) Determine the mass of the car: P = m * g and m = P / g = 50 * 10 ^ 3/10 = 5000 kg.

2) Determine the vehicle acceleration module (slow motion, a <0):

V = V0 + a * t and a = -V0 / t = -10 / 20 = -0.5 m / s ^ 2; | a | = 0.5 m / s ^ 2.

3) Let’s calculate the value of the friction force: | m * a | = | Ftr. |.

Ftr. = 5000 * 0.5 = 2500 N or 2.5 kN.

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