Advertisements
Advertisements
प्रश्न
A boy takes 3 minutes to lift a 20 litre water bucket from a 20 m deep well, while his father does it in 2 minutes. Compare:
- the work, and
- power developed by them.
Advertisements
उत्तर
Mass of bucket m = 20 kg
∵ 1 cm3 of water = 1g
∵ 1000 cm3 = 1 Lit. = 1 kg
Height to which bucket is raised h = 20 m
(i) Work done by boy and father = mgh
= 20 × 9.8 × 20
= 3920 J
∵ Work done is independent of time taken
∴ Ratio of work done = 1 : 1
(ii) Power developed is
`"P"_"boy"/"P"_"father" = ("W"/"t"_"boy")/("W"/"t"_"father") = (3920/180s)/(3920/120s) = 120/180`
`therefore "P"_"boy"/"P"_"father" = 2/3 = 2 : 3`
Power developed by boy : Power developed by father = 2 : 3
APPEARS IN
संबंधित प्रश्न
A boy weighing 40 kgf climbs up a stair of 30 steps each 20 cm high in 4 minutes and a girl weighing 30 kgf does the same in 3 minutes. Compare:
- The work done by them.
- The power developed by them.
A stone of mass m is rotated in a circular path with a uniform speed by tying a strong string with the help of your hand. Answer the following questions
1) Is the stone moving with a uniform or variable speed?
2) Is the stone moving with a uniform acceleration? In which direction does the acceleration act?
3) What kind of force acts on the hand and state its direction?
Give an example when work done by the force of gravity acting on a body is zero even though the body gets displaced from its initial position.
Name the quality which is measured in kW.
A body of mass m is moving with a uniform velocity u. A force is applied on the body due to which its velocity changes from u to v. How much work is being done by the force?
What do you mean by a centrifugal force?
In the following case write yes, if the work is being done and no if no work is being done.
A man trying to push a wall.
A machine raises a load of 750 N through a height of 16 m in 5 seconds. Calculate the power at which the machine works.
A man raises a box of mass 50 kg to a height of 2 m in 20 s, while another man raises the same box to the same height in 50 s. Compare:
- the work done, and
- the power developed by them. Take g = 10 N kg-1
