Question

A ball bounces 80% of its original hieght what fraction of of its mechanical energy is lost in each bounce where is the energy go

Answer 1

Let a ball fall from a height h, 

thenKinetic energy of ball at the time striking the ground= Potential energy of ball at height h

so, K.E=mgh

Kinetic energy of ball due to rebounce will be :

K.Er =P.E of ball at height h1= mgh1

Loss of kinetic energy due to re-bounce=K.E -K.Er

=mgh -mgh1

=mg(h-h1)

=mg(h-80h/100)

=mg(20h/100)

= 0.2 x mgh

Fractional loss in K.E in each re-bounce will be :

=K.E-K.Er/K.E

=0.2 x mgh/mgh

=0.2

=0.2 x100% 

=20%

Fraction of its Mechanical energy lost in each rebound is 20%

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