Question

a child standing at the edge of a cliff 100m high throws a stone vertically downwards. The stone hits the sea 4s later. Ignoring air resistance, find the initial speed with which the stone is thrown
h = -4.9t^2 + vt + 100, where v is the initial velocity

when t = 4, h = 0
0 = -4.9(4) + 4v + 100
4v = -80.4
v = -20.1

the stone was tossed with a velocity of 20.1 m downwards

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