What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
When the satellite moves around the earth, the force of gravity acts on it along the radius of its orbit. The direction of motion is along the tangent to the orbit at any point. Thus, force acts perpendicular to displacement. Therefore, the work done on the satellite is zero.
A certain household has consumed 250 units of energy during a month. How much energy is this in joules?
Energy consumed by the household = 250 units
1 unit of energy = 1 kWh = 3.6 x 106 J
∴ 250 units of energy = 250 x 3.6 x 106
= 9 x 108 J.
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy ? If the object is allowed to fall, find its kinetic energy when it is half-way down.
Does the transfer of energy take place when you push a huge rock with all your might and fail to move it ? Where is the energy you spend going?
While pushing the rock, transfer of muscular energy takes place. This energy is entirely spent in doing work against friction between the rock and the ground.
Since, the rock does not move, no work is done by the body.
What are the various energy transformations that occur when you are riding a bicycle?
For pulling the bicycle, muscular energy is used. Muscular enrgy is further converted into kinetic energy. A part of the muscular energy is used in doing work against friction on the road. This part of the muscular energy changes into heat.
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