Advertisements
Advertisements
प्रश्न
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
उत्तर
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
संबंधित प्रश्न
What is power?
An electric heater is rated 1500 W. How much energy does it use in 10 hours?
Find the energy in joules consumed in 10 hours by four devices of power 500 W each.
Define kilowatt-hour.
Name the physical quantity whose unit is watt.
A body does 1200 joules of work in 2 minutes. Calculate its power.
In an experiment to measure his power, a student records the time taken by him in running up a flight of steps on a staircase. Use the following data to calculate the power of the student :
Number of steps = 28
Height of each step = 20 cm
Time taken = 5.4 s
Mass of student = 55 kg
Acceleration = 9.8 m s−2
due to gravity
In loading a truck, a man lifts boxes of 100 N each through a height of 1.5 m. (g = 10 m s−2)
- How much work does he do in lifting one box?
- How much energy is transferred when one box is lifted?
- If the man lifts 4 boxes per minute, at what power is he working?
In loading a truck, a man lifts boxes of 100 N each through a height of 1.5 m.
How much energy is transferred when one box is lifted?
An electric motor raises a load of 0.2 kg, at a constant speed, through a vertical distance of 3.0 m in 2 s. If the acceleration of free fall is 10 m/s2, the power in W developed by the motor in raising the load is :
