A metal ball of mass 60 g falls on a concrete floor from a vertical height of 2.8 m and rebounds height of 1.3 m. Find the change in K.E. in S.I. units.

Explanation

Potenial energy of ball at height `h_(1)= 2.8m`
`PE_(1)= mgh_(1)= (60)/(1000)xx10xx2.8=1.68J`
`:.` Kinetic energy just before striking the ground = `K.E_(1)= 1.68J`
Potential energy at height `h_(2)= 1.3m`
`P.E_(2)= mgh_(2)= (60)/(1000)xx10xx 1.3m= 0.78 J`
`:. K.E_(2)` just after rebounding = 0.78J
`:.` Change in `K.E= K.E_(1)-K.E_(2)=(1.68-0.78)J=0.9J`