Advertisements
Advertisements
Question
How is the power related to the speed at which a body can be lifted? How many kilograms will a man working at the power of 100 W, be able to lift at a constant speed of 1 m s–1 vertically? (g = 10 m s–2)
Advertisements
Solution
Power associated in lifting a body of mass m upto a height h in time t is,
p = `("mgh")/"t"`
Here, `"h"/"t"` = speed = v
∴ P = mgv
Here P = 100W, v = 1ms−1,10 ms−2
m = `"P"/"gv"`
So, m = `(100 "W")/(10 "ms"^-2 xx 1 "ms" ^-1)`
= 10 kg
APPEARS IN
RELATED QUESTIONS
Define average power.
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
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.
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?
How much is the mass of a man if he has to do 2500 joules of work in climbing a tree 5 m tall? (g = 10 m s−2)
Define kilowatt-hour.
Name the physical quantity whose unit is watt.
The power output of an engine is 3kW. How much work does the engine do in 20 s?
A car of weight 20000 N climbs up a hill at a steady speed of 8 m/s, gaining a height of 120 m is 100 s. Calculate : power of engine of car.
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
