Answer the following:
a) The casing of a rocket in flight burns up due to friction. At whose expense is the heat required for burning obtained? The rocket or the atmosphere?
b) Comets move around the sun in highly elliptical orbits. The gravitational force on the comet due to the sun is not normal to the comet's velocity in general. Yet the work done by the gravitatonal force over every complete orbit of the comet is zero. Why?
c) An artificial satellite orbiting the earth in very atmosphere loses its energy grdually due to dissipation against atmospheric resistance, howerver small. Why then does its speed increase progressively as it comes closer and closer tothe earth? d)In fig i) the man walks 2m carrying a mass of 15 kg on his hands. In Fig ii) he walks the same distance pulling the rope behind him. The rope goes over pulley, and a mass of 15 kg hangs at its other end. In which case is the work done greater?

Explanation

As the casing of a rocket burns , the mass of roocket decreases . Thus , the heta energy required for burning of rocket is obtained from the rocket itself .
(b) Work done by the gravitational force is zero as th gravitational force si a conservative force . Wrok done by this over a closed path of any shape is zero .
(c ) As the satellite comes closer to the earth its potential energy starts decreasing whereas its kinetic energy and its kinetic energy and potential energy is constant . However . total energy of the satellite decreases due th dissipation against atmospheric resistance friction .
(d) In the first case , teh force is applied by the man in vertically upward direction but the displacement of the block is along the horizontal direction .
` :. ` Work done = `Fs cos 90^(@) = 0 `
In second case , both the applied force and the displacement of the block are along the same direction .
Therefore `theta = 0 ^(@)`
` :. " " W = Fs cos theta `
` = 15 xx 9.8 xx 2xx 1 = 294 J `
Work done in the `2^(nd)` case is larger .