1:21 AM C 29%, D ooo Verizon session masteringphysics.com C Phy 201 Spring 2016

Question

1:21 AM C 29%, D ooo Verizon session masteringphysics.com C Phy 201 Spring 2016 Night Problem 444 Police investigators, examining the scene of an accident involving two cars, measure 64-m-long skid marks of one of the cars, which nearly came to a stop before coliding. The coefficient of kinetic friction between rubber and the pavement is about 0.72. Estimate the initial speed of that car assuming a level road. Express your answer to two significant figures and include the appropriate units. Submit My Answers Give up

Explanation / Answer

By Work energy theorem ,the work done by frictional force is equal to change in Kineitc energy of the car

Wfriction =KEfinal-KEinitial

Since the car comes to rest ,the final speed is zero ,so the final kinetic energy is also zero.

-Ffrictiond =0-(1/2)mVinitial2

since work done by frictional has negative sign since the direction of force is opposite to direction of motion.

usmg*d =(1/2)mVinitial2

usg*d =(1/2)Vinitial2

0.72*9.8*64 =(1/2)*Vinitial2

Vinitial=30.05 m/s

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