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2014-10-05T20:44:31+05:30

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At h = 10m, 
PE = mgh = 10mg
KE = 0, 
Total Energy (TE) = 10mg

Just before impact,
PE = 0
KE = TE - PE = 10mg

After impact, energy lost = 20%
energy lost = 20% of 10mg = 2mg
Total Energy Left (TE)= 10mg - 2mg = 8mg

Let after impact it reaches a maximum height = H
At height H
KE = 0 (as velocity is 0 at maximum height)
PE = mgH
But PE = TE = 8mg
Thus mgH = 8 mg
or H=8m

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