The kinetic energy is given by:

We know the mass and the maximum speed, plugging their values in the expression above we have:

Therefore, the answer is d.
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Explanation:
Load (l) = 680N
Effort (E) = 500N
Length slope (l) = 12m
Height slope (h) = 8 m
Output = load * height
680 *8 = 5.44 *103 J
The Input = effort * length = 500 *12 = 6000J
the Mechanical advantage (M.A) = load effort= 600500=1.36
the Velocity ratio (V.R) =lh=128 = 1.5
the Efficiency =M.A100%V.R= 90.6%
Hi am not sure but have searched on online
Depending on the height of the building they can break due to impact on the floor.