A ball is dropped from a height of 10m. If the energy of the ball reduces by 40% after striking the ground, how much high can the ball bounce back ?
on reaching the ground the energy of the object = the energy at the top [law of conservation of mass]
energy at the top = potential energy = mgh
= m*10*10 = 100x joule [ let mass be x]
loss of energy = 40% of 100x J
energy left = 60% of 100x
= 60/100 * 100x = 60x
now the energy of the object on reaching the top again will be equal to that at the surface = 60x
bt height will differ
Ep = mgh = x*10*h
60x = 10xh
60x / 10x = h
h = 6 meter
:. the ball bounce back to 6m...