Advertisements
Advertisements
Question
A boy weighing 350 N climbs up 30 steps, each 20 cm high in 1 minute, Calculate:
- the work done and
- power spent.
Advertisements
Solution
Force = weight of body = 350 N
Total distance = h = 30 × 20 = 600 cm
h = `600/100 = 6m`
(i) Work done W = F × h
W = 350 × 6 = 2100 J
(ii) Power spent = `"Work done"/"Time taken" = (30 × "Mg" × "h")/(1 " minute")`
= `((30 × 350 ×20)/100)/(1 " minute")`
= `(2100 J)/(1 " minute")`
= `(2100 J)/(60 " Sec")`
Power spent = 35
APPEARS IN
RELATED QUESTIONS
Give the expression for mechanical advantage of an inclined plane in terms of the length of an inclined plane.
Name the force needed for circular motion. What is the direction of the force?
A pump is used to lift 600 kg of water from a depth of 75 m in 10s. Calculate:
- The work done by the pump,
- the power at which the pump works, and
- The power rating of the pump if its efficiency is 40%. (Take g = 10m s-2).
`["Hint" : "Efficiency" = "useful power"/"power input"]`
A man raises a box of mass 50 kg to a height of 2 m in 20s, while another man raises the same box to the same height in 50s. Calculated:
- the work done, and
- the power developed by each man. Take g = 10 N kg-1.
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.
What do you understand by work? Is work a scalar or a vector quantity?
A force F when acts on a body, displace it by a distance d in a direction at an angle θ with the direction of the force. Write down the expression for the work done by the force.
What is the S.I. unit of work? Define it.
What happens to the power if the time for doing work is reduced from t second to t/10 second?
A coolie carrying a load on his head and moving on a frictionless horizontal platform does no work. Explain the reason why.
