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)

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