UP AND DOWN THE HILL. A 28.00 kg rock approaches the foot of a hill with speed o

Question

UP AND DOWN THE HILL. A 28.00 kg rock approaches the foot of a hill with speed of 15 m/s. This hill slopes upward at a constant angle of 40 degree above the horizontal. The coefficient of static and kinetic friction between the hill and the rock are .75 and 0.20, respectively. a) Use energy conservation to find the maximum height above the foot of the hill reached by the rock. b) Will the rock remain at rest at its highest point , o will it slide back down the hill? c) If the rock does slide back down, find its speed when returns to the bottom of the hill

Explanation / Answer

a) KE - energy lost in friction = final PE

3150 - 28*9.8*0.20*hcos40/sin40 = 28*9.8*h

h = 9.27 m m

b) mgsin40 >s * mgcos40

mass rolls down

0.5mV^2 = mgh - 28*9.8*0.20*hcos40/sin40

V = 11.76 m/s

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