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When does a force do work?
State the condition when the work done by a force is positive. Explain with the help of examples.
State two factors on which power spent by a source depends. Explain your answer with examples.
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 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.
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 coolie carries a load of 30 kgf through a distance of 500 m in 5 minutes while another coolie B carries the same load through the same distance in 10 minutes. Compare the
(i) work done, and
(ii) power developed. (Take: g = 10md−2)
For the following scenarios, state whether the work done by gravity is positive, negative, or zero.
A person climbs a ladder.
