Engineering
Physics
Conservation of Energy
Question

A ball is dropped from a height h. As it bounces off the floor, its speed is 80 percent of what it was just before it hit the floor. The ball will then rise to a height of most nearly

0.75 h

0.64 h

0.50 h

0.80 h

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Solution

Speed becoming 80% means kinetic energy becomes 64% just before collisions that means

mgh'=64100mgh    h'=0.64 h.