Advertisements
Advertisements
Question
A boy of mass 40 kg climbs up the stairs and reaches the roof at a height 8 m in 5 s. Calculate:
- the force of gravity acting on the boy,
- the work done by him against the force of gravity,
- the power spent by boy. (Take g = 10 m s-2)
Advertisements
Solution
Mass of boy = 40 kg, Vertical height moved, h = 8 m, Time taken, t = 5s.
(i) Force of gravity on the boy F = mg
= 40 kg × 10 m/s-2
= 400 N
(ii) Work done against gravity, W = mgh
= 400 × 8
= 3200 J
(iii) Power = `"work"/"Time" = "mgh"/"t"`
`= (3200 " J")/(5 " s")`
= 640 W
APPEARS IN
RELATED QUESTIONS
Power spent by a body depends on the time for which it does work.
A body, when acted upon by a force of 10 kgf, moves to a distance 0.5 m in the direction of force. Find the work done by the force. Take 1 kgf = 10 N.
Name five appliances or machines which use an electric motor.
A girl of mass 50 kg runs up a flight of 40 steps in 20 seconds. If each step in 20 cm high, calculate the power developed by the girl. (g= 10 ms-2).
Can two agents, doing the same work, have different power?
Explain, why submarines are able to dive underwater as well as a sail on the surface of the water?
The work done by the heart is 1 Joule per beat. Calculate the power of the heart if it beats 72 times in one
