a ball is dropped from a height of 10m. if the energy of the ball reduces by 40 percent after striking the ground,how much high the can the ball bounce back

Here, ball has a potential energy due to its height from the floor i.e. mgh = 10m

According to question,

mgh'=mgh x 60/100

(Since ball losses 40% of its energy ,so it is left with 100-40=60% of energy)

Therefore h'=h x (60/100)

=10 x 60/100=6m