A bread gives a boy of mass 40kg of energy 21KJ.If the efficiency is 28% the the height can be climbed by using this energy is:
(A)22.5 m
(B)15 m
(C)10 m
(D)5 m
28% of energy of bread is available to climb
∴ 28% of 21 kJ = 5.88kJ
By climbing energy form bread is converted to potential energy of boy = mgh
∴ 5.88kJ = mgh
on substituting m = 40 kg, g=9.8 m/s2
Answer: (b)