Question

please answer it very fastly

Answer 1

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*30=300mJoule
loss of energy=40% of 300mJ
energy left=60% of 300m
=60/100*300m=180m
Now the energy of the object on reaching the top again will be equal to that of the surface=180m
but h will differ
Ep=mgh=m*10*h
180m=10mh
therefore,h=18m

Answer 2

Since we know that

Energy (E ) = m×g×h

As it has been given that
h = 30 m

So, E= mg×30
=30mg ..............(1)


Again ,

Energy after striking ,
=E-40%of E
= E-40/100×E
=60/100E


Now ,
Energy after striking = mgh
60/100E = mgh
E=100/60mgh

From (1) we have :

30mg=100/60mgh
h =30×60/100
=18 m