
Arturo O. answered 07/30/17
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At the bottom, the kinetic energy of the teacher should be
K = mgh = (70 kg)(9.8 m/s2)(6.0 m) = 4116 J
But he has a final speed v of 7.0 m/s, so
K' = (1/2)mv2 = (1/2)(70.0)(7.0)2 J = 1715 J
He lost K - K'.
K - K' = (4116 - 1715) J = 2401 J.