Advertisements
Advertisements
Question
A boy weighing 40 kg carries a box weighing 20 kg to the top of a building 15 m high in 25 seconds. Calculate the power. (g = 10 m/s2)
Advertisements
Solution
Mass of the boy, (m1) = 40 kg
Mass of the box, (m2) = 20 kg
Height, (h) = 15 m
Acceleration due to gravity, (g) = 10 m/s2
Time taken, (t) = 25 s
Total mass of the system,
M = m1 + m2
=> M = 40 + 20 = 60 kg
So, work done by the boy is,
W = mgh
=> W = (60)(10)(15)
=> W = 9000 J
Now, we can calculate the power of the boy as,
Power = `"Work done"/"Time"`
So ,
Power = `9000/25` W
= 360 W
So, the power is 360 W.
APPEARS IN
RELATED QUESTIONS
A battery lights a bulb. Describe the energy changes involved in the process.
What is the work done by the force of gravity on a satellite moving round the earth? 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.
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.
A trolley is pushed along a road with a force of 400 N through a distance of 60 m in 1 minute. Calculate the power developed.
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.
If the man lifts 4 boxes per minute, at what power is he working?
(g = 10 m s−2)
