A car with a mass of 2 tons brakes and stops after 4 s, having covered a distance of 40 m.
| September 4, 2021 | education
A car with a mass of 2 tons brakes and stops after 4 s, having covered a distance of 40 m. What work does the friction force perform in this case?
The final speed of the car is zero, so the path s, acceleration a and time t are related by the equation
s = 0.5at ^ 2, whence
a = 2s / t ^ 2 = 2 * 40/4 ^ 2 = 5 m / s ^ 2.
According to Newton’s second law, the friction force F that braked the car is equal to the mass m = 2 m = 2000 kg of the car, multiplied by the acceleration a:
F = ma = 2000 * 5 = 10000 N = 10 kN.
The work A of the friction force is equal to the force F multiplied by the path s:
A = Fs = 10 * 40 = 400 kJ.
Answer: 400 kJ.
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