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11. In an accident a freeway sports car made skid marks 200 m long along the pavement. The police estimated the braking acceleration of the car to be – 0.8g under the road conditions prevailing. Determine the speed of the sports car when the brakes were applied.

• mechanical science -

Kinetic energy loss equals work done against skidding friction. The mass M cancels out.

The friction force F can be deduced from the mass and acceleration.

(M/2) V^2 = (0.8g)*M*X
V^2 = 1.6 *g*200

V = 56 m/s = 201.6 km/s = 125 mph

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