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.
How much work each does? Take density of water = 103 kg m-3 and g = 9.8 N kg-1.
उत्तर
Work done = mgh
Given,
density of water = 103kg m -3
To convert, density of water to mass per litre
We know, 1 litre = 1000 cm3 and 1 m3 = 106 cm3
So, `10^3 kgm^-3 = (1000 " kg")/(1 "m"^3)`
`= (1000 " kg")/(10^6 cm^3)`
`= (1 kg)/(1000 cm^3)`
`= (1 kg)/(1 litre)`
Hence, 20 L of water = 20 Kg by mass
height = 20 m
Now, substituting the values in the formula for work done we get
W = 20 × 9.8 × 20
W = 3.92 kJ
APPEARS IN
संबंधित प्रश्न
When a body moves in a circular path, how much work is done by the body? Give reason.
(Hint: The body is acted upon by the centripetal force.)
What is meant by a rotatory motion? Give one example.
A body is provided at a point. A force of 20 N is applied at a distance of 40 cm from the pivot. Find the moment of force about the pivot.
How much force is applied on a body when 150 J of work is done in displacing the body through a distance of 10 m in the direction of the force?
Work done by a force is equal to the product of ....... and ....
Define one newton. Write the relation between the S. I. unit and the C.G.S. unit of force.
Calculate the work done when:
A car is moved on a rough road through 30 m against a frictional resistance of 75 N.
A force of 1 kgf displaces a body by a distance of 10 cm
(i) in direction of force,
(ii) normal to the force
(iii) at an angle of 60° to the direction of the force.
Calculate the amount of work done in each case. (Take: g = 9.8 ms−2 )
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
