# Work Energy Power Numerals Part 1

1) A body, when acted upon by a force of 10 kgf, gets displaced by 0.5 m. calculate the work done by the force, when the displacement is (i) in the direction of force, (ii) at an angle of 60 with the force, and (iii) normal to the force.

2) A body of mass 40 kg climbs up the stairs and reaches the roof at a height 8 m in 5 s. Calculate : (i) the force of gravity acting on the body (ii) the work done by him against the force of gravity (iii) the power spent by the boy. (Take g = 10 m s-2)

3) A man spends 6.4 kJ energy in displaying a body by 64 m in the direction in which he applies force, in 2.5s. Calculate: (i) the force applied, and (ii) the power spent (in H.P.) by the man.

4) A weight lifter lifted a load of 200 kgf to a height of 2.5m in 5s. Calculate : (i) the work done, and (ii) the power developed by him. Take g = 10 N kg-1.

5) A machine rises a load of 750 N through a height of 16 m in 5 s. Calculate : (i) the energy spent by the machine (ii) the power of machine if it is 100 % efficient.

6) An electric heater of power 3 kW is used for 10 h. How much energy does it consume? Express your answer in (i) kWh, (ii) joule.

7) A water pump raises 50 litre of water through a height of 25m in 5 s. Calculate the power of the pump required. (Take g = 10 N Kg-1 and density of water = 1000 kg m-3)

8) A pump is used to lift 500 kg of water from a depth of 80 m in 10 s. Calculate : (a) The work done b the pump (b) the power at which the pump works, and (c) the power rating of the pump if its efficiency is 40% (take g=10 m s-2)  [ Hint : Efficiency =  ]

9) An ox can apply a maximum force of 1000 N. It is taking part in a cart race and is able to pull the cart at a constant speed of 30 m s-1 while making its best effort. Calculate the power developed by the ox.

10) The power of a motor is 40 kW. At what speed can the motor raise a load of 20000 N ?

11)  Rajan exerts a force of 150 N in pulling a cart at a constant speed of 10 m s-1. Calculate the power exerted.

12) A boy weighing 350 N climbs up the 30 steps each 20 cm high in 1 minute. Calculate : (i) the work done, and (ii) the power spent.

13) It takes 20 s for a person A of mass 50 kg to climb up the stairs, while another person B of same mass does the same in 15 s. Compare the (i) work done, and (ii) power developed by the person A and B.
Ans: As person A and B has same mass and climb same height against the gravity, therefore the work done (W) by them is same.

14) A body of weight 40 kgf climbs up the 15 steps, each 15cm high in 10s and a girl of weight 20 kgf does the same in 5s. Compare the (i) work done, and (ii) the power developed by them. Take g = 10 N kg-1.

15) A man raises a box of mass 50 kg to a height of 2m in 20 s, while another man rises the same box to the same height in 50 s. (a) compare : (i) the work done, and (ii) the power developed by them.
(b) Calculate : (i) the work done, and (ii) the power developed by each man. Take g = 10 N Kg-1.

16) A boy takes 3 minutes to lift a 20 litre water bucket from a 20m deep well, while his father does it in 2 minutes. (a) compare : (i) the work, and (ii) power developed by them. (b) How much work each does? Take density of water = 103 kg m-3 and g = 9.8 N kg-1.

For Answer’s see below :

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