1.

When a ball is freely fallen from a given height it bounces to 80%

Answer»

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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