# After turning off the engine, the car stopped after 3 seconds.

After turning off the engine, the car stopped after 3 seconds. The resistance force acting on the car during braking is 6000 N. The weight of the car is 900 kg. What was the initial speed of the car?

t = 3 s.

Fcopr = 6000 N.

m = 900 kg.

V = 0 m / s.

V0 -?

Let’s write 2 Newton’s law for a car when braking: Fcopr = m * a.

The formula for the definition for the acceleration of the body: a = (V0 – V) / t.

Since the car has stopped, the final speed will be 0, V = 0 m / s.

a = V0 / t.

Fcopr = m * V0 / t.

The formula for determining the initial speed will be: V0 = Fcopr * t / m.

V0 = 6000 N * 3 s / 900 kg = 20 m / s.

Answer: the initial speed when braking the car was V0 = 20 m / s.

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