Question

An apple gives 21 kj energy to a boy. How much height he can climb by using this energy. If his efficiency is 28%? (mass of boy 40kg)

Answer 1

Dear Student,

◆ Answer -

Height = 15 m

● Explanation -

# Given -

Energy supplied by apple = 21 kJ = 21000 J

Mass of the boy = 40 kg

# Solution -

Actual energy available to the boy is -

Available energy = energy supplied × efficiency

Available energy = 21000 × 28/100

Available energy = 5880 J

This energy will get converted to potential energy of boy when he climbs -

Potential energy = mass × gravity × height

5880 = 40 × 9.8 × height

Height = 5880 / 392

Height = 15 m

Therefore, boy can climb upto 15 m on thr tree.

Hope this helps you...

Answer 2

Here : Energy of one apple =2112J

=21×10

3

J

Efficiency of the boy =28%=0.28

Mass of the boy m=40kg

Here the actual energy consumed by the boy is given by as

=0.28×21000=5880J ...(1)

and the energy consumed by the boy in climbing h meter height is given by

=mgh=40×9.8×hJ ...(2)

Equating equations (1) and (2) we get

40×9.8×h=5880J

h=

40×9.8

5880

=15m