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# M2 work,energy and power watch

1. I serously dont know whats wrong with me today... maybe its too late *yawn*. Could someone please help me with this question

A boy and his skateboard have a mass of 50kg. He descends a slope inclined at 12 degrees to the horizontal starting from rest. At the bottom, the ground becomes horizontal for 10m before rising at 8 degrees to the horizontal. The boy travels 30m up the incline before coming to rest again. He is subject to a constant resistance of 20N throughtout the motion, By modelling the boy and his skateboard as a single particle find the distance the boy travelled down the slope.
2. see attachment:
total distance travelled = H/sin12 + 10 + 30
Work of Resistance = 20 x (H/sin12 + 40)

ΔKE + ΔPE = W_ext.
ΔKE = 0
ΔPE = mgΔh = mg(h_2 - h_1) = 50.g.(30sin8 - H)

50.g.(30sin8 - H) = 20 (H/sin12 + 40)
solve and find H.

Edit: forgot that the question wanted the distance travelled down the slope: do it's H/sin12.
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