Why would you assume velocity is constant? There is so much wrong with you answe

Question

Why would you assume velocity is constant? There is so much wrong with you answer it is hard to pick where to start! First of all, the ball was dropped from rest- in other words, initial velocity is 0. Also, if velocity were constant than the acceleration would have to be 0. In your words,"only gravity does work on it" - gravity ,I hope you know, is an acceleration that is not 0.  Your conjecture violates Newton's law of motion, defies gravity.  If the Gravitational Potential Energy were the only thing changing (trust me it is not) than where has the energy gone when it is zero? You might want to know, Kinetic Energy is simply converted into Gravitational Potential Energy. 

Explanation / Answer

given mass of rubber ball = m = 0.650kg intial height = 2.50m then intial mechanical energy = mgh                                            = 0.650kg *9.8m/s2 *2.50m = 15.9J the seconed height = 0.75*2.50m = 1.875m then seconed mechanical energy = mgh = 0.650kg*9.8*1.875 = 11.9J    losses energy = 15.9J - 11.9J = 4.0J this energy converted as thermal energy in the third heigth = 0.75 *1.875m = 1.40m    third mgh = 8.9J losses energy = 11.9J - 8.9J = 3.0J on seconedbounce.

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