physics class 12

Question

a man whose mass is m kg vertically jumps into air from a sitting position in which his centre of mass is at a height h1 from ground . when his feet are just about to leave the ground his centre of mass is h2 from the ground and finally rises toh3 when he is at the top of the jump.(a) what is upward force exerted by the ground on him treating hima as constant (b) find work done by normal reaction on ground

Answer 1

The work of upward force changes the man’s potential energy so that his center of mass moves from h₁ to h₂, and provides him kinetic energy, which allows him to reach the height h₃. At the same time, the man’s kinetic energy at the height h₃ is zero. Thus, according to the conservation of energy, all the work is spent to change the man’s potential energy:

W=mgΔh₁₃=mg(h₃-h₂)J..........(1)

The work is performed while the center of man’s mass moves from h₁ to h₂, thus:

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