(a) The kinetic energy of the cart when it moves is 2/3 the way down is 1/3mgh.
(b) The total mechanical energy of the cart at the given height of 5 m is 5mg.
The potential energy of the cart when it is 2/3 way down the given height of 5 m is calculated as follows;
ΔP.E = mghf - mgh₀
ΔP.E = mg(hf - h₀)
ΔP.E = mg(2h/3 - h)
ΔP.E = -¹/₃mgh
ΔK.E = -ΔP.E
ΔK.E = ¹/₃mgh
M.A = P.E + K.E
M.A = ²/₃mgh + ¹/₃mgh
M.A = mgh
M.A = mg(5)
M.A = 5mg
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