A car with a mass of 1 tonne starts to move, and moving uniformly accelerated, in 20 seconds picks up a speed of 72 km / h.

A car with a mass of 1 tonne starts to move, and moving uniformly accelerated, in 20 seconds picks up a speed of 72 km / h. What is the work done by the car engine if the average resistance force acting on the car is 500 N?

m = 1 t = 1000 kg.

V0 = 0 m / s.

t = 20 s.

V = 72 km / h = 20 m / s.

Fcopr = 500 N.

∠α = 0 °.

A -?

The mechanical work A of the force F is determined by the formula: A = F * S * cosα, where S is the movement of the body under the action of the force, ∠α is the angle between the direction of the force F and the movement of S.

Let’s write 2 Newton’s law for the car: m * a = F – Fcopr.

F = m * a + Fc.

a = (V – V0) / t.

S = V0 * t + a * t ^ 2/2.

Since V0 = 0 m / s, then a = V / t, S = a * t ^ 2/2 = V * t / 2.

cos 0 ° = 1.

A = (m * V / t + Fcopr) * V * t / 2.

A = (1000 kg * 20 m / s / 20 s + 500 N) * 20 m / s * 20 s / 2 = 300000 J.

Answer: the car engine does work A = 300,000 J.