Advertisements
Advertisements
Question
(a) Define power and name its unit.
(b) A girl weighting 50 kg climbs up 60 steps each of 20 cm height in 5 minutes. Calculate the power developed.
Solution
(a) The rate of doing work is called power.
SI unit of power = watt
CGS unit of power = erg per second
(b) Given mass = 50kg
Total height traveled = 60 x 20 cm = 1200 cm = 12m
g = 10 ms-2
time taken = 5 min = 5 x 60 s = 300 s
Work done = mgh = 50 x 10 x 12 = 6000J
Power = `"work done"/"time taken" = 6000/300` = 20 watt
APPEARS IN
RELATED QUESTIONS
What is the work done by the moon when it revolves around the earth?
.A man raises a box of mass 50kg to a height of 2m in 20s, while another man raises the same box to the same height in 50s. Compare:
(i) the work done, and
(ii) the power developed by them.
State the energy transformation on the following:
Electricity is obtained from solar energy.
What are the quantities on which the amount of work done depends? How are they related to work?
A boy throws a rubber ball vertically upwards. What type of work, positive or negative, is done : by the force applied by the boy?
(a) by the force applied by the boy?
(b) by the gravitational force of earth?
When is the work done by a force on a body : (a) positive, (b) negative, and (c) zero?
Why is the work done on an object moving with uniform circular motion zero?
A man carrying a suitcase in his hand is walking horizontally. What is the work done against gravity?
A boy pulls a box up to 10 m with a force of 5 kgf. Calculate the work done by him.
Define energy and state the unit of energy and the law of conservation of energy.
A bullet is of mass 'm' g and is moving with a velocity 'v' m/s. Find the kinetic energy of the bullet when
(a) The mass is doubled,
(b) The velocity is tripled.
Why is less effort needed to lift a load over an inclined plane as compared to lifting the load directly?
What are the advantages and disadvantages of using solar cells for producing electricity?
Calculate the work done when:
A 5 kg weight is lifted 10 m vertically. (g = 9.8 m/s2)
An electric motor pump is 60% efficient and is rated 2.5 H.P. Calculate the maximum load it can lift through a height of 10m in 8 sec. (1 H.P. = 750 W).
A car is accelerated on a levelled road and attains a velocity 4 times of its initial velocity. In this process the potential energy of the car
