Physics Question

[HopefulOncoDoc]

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Could someone please explain to me why these answers are correct? Thanks a lot!

A car traveling on a dry road at 10 m/s comes to a stop (uk = 0.5). If the same car were instead traveling on a wet road (uk = 0.2), how does the work required to stop the car on the wet road, Wwet, compare to the work required to stop the car on the dry road, Wdry?

A. Wdry = 2Wwet
B. Wdry = sqrt(2)Wwet
C. Wdry = Wwet
D. Wwet = 2Wdry

The answer is C

Which of the following factors will NOT impact the kinetic energy of an object sliding down a slope?

A. The height of the slope
B. The length of the slope
C. The coefficient of kinetic friction (uk)
D. The coefficient of static friction (us)

The answer is D

 

[Morsetlis]

The first one is a conservation of energy. To bring an object to a stop, the kinetic energy has to all be shed. The lower coefficient of friction would increase impulse time needed to reduce the momentum, but the total amount of energy needed to be shed would not be changed.

The second one signifies that the coefficient of static friction does not factor into .5mv^2. Here, v is modulated by the force of friction, which while moving has to do with the coefficient of kinetic friction and the normal force, which is regulated by height and length of the slope.