A 2400 kg car moving at an initial speedof 20 m/s along a horizontal road skids

Question

A 2400 kg car moving at an initial speedof 20 m/s along a horizontal road skids toa stop in 66 m. (Note: Whenstopping without skidding and using conventional brakes, 100percent of the kinetic energy is dissipated by friction within thebrakes. With regenerative braking, such as that used in hybridvehicles, only 70 percent of the kinetic energy is dissipated.) (a) Find the energy dissipated by friction.
kJ

(b) Find the coefficient of kinetic friction between the tires andthe road.
(a) Find the energy dissipated by friction.
kJ

(b) Find the coefficient of kinetic friction between the tires andthe road.

Explanation / Answer

mass m = 2400 kg

Initial speed u = 20 m / s

Distance travel before stop S= 66 m

Energy dissipated by friction E = net work done

                                                   = change in kinetic energy   Since from work energytheorem

So, E = ( 1/ 2) m[ u ^ 2- v ^ 2]

Where v = final speed = 0

Plug the values we ge E =480000 J

                                   = 480 kJ

(b). frictional force F = E / S

                                   = 7272.72 N

We know   F = mg

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