A car weighing 2 tons moved at a speed of 36 km / h. 10 meters before the pedestrian crossing, the driver noticed

| September 27, 2021 | education

A car weighing 2 tons moved at a speed of 36 km / h. 10 meters before the pedestrian crossing, the driver noticed a pedestrian and began to brake, stopping right in front of the crossing. Find the coefficient of wheel friction on the asphalt.

With a mass m = 2 t = 2000 kg and a speed v = 36 km / h = 36000/3600 m / s = 10 m / s, the car had kinetic energy

Ek = mv ^ 2/2 = 2000 * 10 ^ 2/2 = 100000 J.

After stopping, this energy turned to 0, for which the work of the friction force, equal to Ek, was spent. That is, the work Am = Fts of the friction force Ft on the path s = 10 m should be equal to the energy Ek

Fтs = Ek, whence

Ft = Ek / s = 100000/10 = 10000 N.

Dividing the force Ft by the weight mg of the car gives the desired coefficient of friction:

k = Ft / (mg) = 10000 / (2000 * 9.8) = 0.51.



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