Advertisements
Advertisements
प्रश्न
Four men lift a 250 kg box to a height of 1 m and hold it without raising or lowering it.
(a) How much work is done by the men in lifting the box?
(b) How much work do they do in just holding it?
(c) Why do they get tired while holding it? (g = 10 m s–2)
Advertisements
उत्तर
Mass of the box, m = 250 kg
Height up to which it is raised, h = 1 m
(a) Work done by the men in lifting the box
= F.s = 250 × 10 × 1 J
(Here F = mg, s = h)
= 2500 J
(b) In just holding the box, there is no displacement, so no work is done.
(c) In order to hold the box at a certain height, men are applying a force that is equal and opposite to the gravitational force acting on the box. While applying the force, muscular effort is involved.
So, men get tired while holding it.
APPEARS IN
संबंधित प्रश्न
What are the various energy transformations that occur when you are riding a bicycle?
State the energy changes in the following case while in use:
A ceiling fan
State the energy changes in the following while in use A loudspeaker .
State the energy changes in the following while using a microphone.
State the energy changes in the following while using an electric motor.
State the energy changes that occur in the following :
An electric generator (or dynamo).
State the energy changes in the following case while in use:
An electromagnet.
A boy is moving on a straight road against a frictional force of 5 N. After travelling a distance of 1.5 km he forgot the correct path at a roundabout (Fig. 11.1) of radius 100 m. However, he moves on the circular path for one and half-cycle and then he moves forward up to 2.0 km. Calculate the work done by him.
Can any object have mechanical energy even if its momentum is zero? Explain.
Can any object have momentum even if its mechanical energy is zero? Explain
