A 1700 kg car moving at an initial speed of 20 m/s along a horizontal road skids
ID: 1421623 • Letter: A
Question
A 1700 kg car moving at an initial speed of 20 m/s along a horizontal road skids to a stop in 54 m. (Note: When stopping without skidding and using conventional brakes, 100 percent of the kinetic energy is dissipated by friction within the brakes. With regenerative braking, such as that used in hybrid vehicles, 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 and the road.
_____
Explanation / Answer
KE of car=1/2mv^2, where KE is the kinetic energy given in J, m is the mass in kg, and v is the velocity in m/s.
Substitute given values:
KE=1/2*1700*20^2
=340,000N
therefore the energy dissipated by friction. 340KJ
KE=Work =F.x=F.54
F=6296.29 N
Coefficient of Kinetic friction, u:
F=uR, where F is the force of friction and R is the Normal to the road surface exerted by the weight of the car
Substitute given values:
15000=u1700*9.8
coefficient of friction u=0.3779
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