I tried to relate them with work and energy, but I still have it wrong In one of

Question

I tried to relate them with work and energy, but I still have it wrong

In one of our snowy Chicago winter days, a bobsled run leads down a hill as sketched in the figure above. The bobsled starts from rest at point A and it's mass of the bobsled, including drive is 150 kg. All along the hills, between points A and D, friction is negligible, but at the end of the run between points D and E, the coefficient of kinetic friction is mu k = 0.4 1) What is the speed of the bobsled at point B) 2) What is work done by gravity between A and C ? 3) Find the distance x beyond point D at which the bobsled will come to a halt

Explanation / Answer

from A to E

work done by friction Wf = -uk*m*g*x

change in potential energy dU = U2 - U1 = -m*g*hA

work done by gravity Wg = -dU = m*g*hA

change in KE = 0

Wg + Wf = dKE

m*g*hA - uk*m*g*x = 0

x = hA/uk

x = 50/0.4

x = 125 m

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