Question

a boy weights 200kg to what height shoduld be raised so ot pe may be 9800

Answer 1

potential energy =mgh

9800=200×9.8×h

h=98000/98×200

h=1000/200

h=5m

hope it helps

Answer 2

Mass = 200 kg 
height = h (say)
g = 9.8 m/s^2 
now 
PE = 9800 J 
200 x h x 9.8 = 9800
h = ( 98 x10 )/ (98 x 2)
h = 5 m