V^2 = Vo^2 + 2a*d = 0.
30^2 + 2a*0.1 = 0, 0.2a = -900, a = -4500 m/s^2.
F = M*a = 0.1 * (-4500)= -450 N.
a ball of mass 100g is dropped from the top of a vertical cliff 45m high. Given that the velocity just before striking the sandy beach is 30m/s and the ball penetrates the sand to a depth of 10cm. Determine its average retardation force
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