Advertisements
Advertisements
Question
A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.
Advertisements
Solution
Work is done whenever the given two conditions are satisfied:
- A force acts on the body.
- There is a body displacement by applying force in or opposite to the direction of force.
- A person holding a bundle of hay on his head becomes exhausted due to muscular weariness. This tiredness is caused by converting chemical energy into heat energy via muscular effort. The guy has done no work because his exertion does not cause the bundle over his head to move, i.e., s = 0.
APPEARS IN
RELATED QUESTIONS
A battery lights a bulb. Describe the energy changes involved in the process.
Calculate the work done by the brakes of a car of mass 1000 kg when its speed is reduced from 20 m/s to 10 m/s?
A body of mass 100 kg is lifted up by 10 m. Find :
(i) the amount of work done
(ii) potential energy of the body at that height (value of g = 10 m/s2)
Define kilowatt-hour.
What is the power of a body which is doing work at the rate of one joule per second?
A body does 1200 joules of work in 2 minutes. Calculate its power.
Fill in the blanks with suitable words :
One watt is a rate of working of one ___________ per ___________.
The power output of an engine is 3kW. How much work does the engine do in 20 s?
An electric heater uses 600 kJ of electrical energy in 5 minutes. Calculate its power rating.
In loading a truck, a man lifts boxes of 100 N each through a height of 1.5 m.
If the man lifts 4 boxes per minute, at what power is he working?
(g = 10 m s−2)
