An 80.0-kg man jumps from a height of 2.50 m onto a platform mounted on springs.

Question

An 80.0-kg man jumps from a height of 2.50 m onto a platform mounted on springs. As the springs compress, he pushes the platform down a maximum distance of 0.240 m below its initial position, and then it rebounds. The platform and springs have negligible mass. Part A What is the man's speed at the instant he depresses the platform 0.120 m? Submit My Answers Give Up Incorrect; Try Again; 4 attempts remaining Part B If the man just steps gently o platform, what maximum dist would he push it down? submit My Answers Give Up

Explanation / Answer

part A
P.E. of man = mgh = 80*9.8*2.5 = 1960 J
1960 = 0.5*k*0.24^2
k = 68055.55 N/m
At the instant, let velocity be v
0.5mv^2 + mgh' + 0.5kx'^2 = 1960
0.5*80*v^2 + 80*9.8*0.12 + 0.5*68055.5*(0.12)^2 = 1960
v = 3.637 m/s

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