ntThe casing of a rocket in flight burns up due to friction .At whose expense is the heat energy required for burning obtained?The rocket or the atmosphere?n

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Answer the following :

(a) The casing of a rocket in flight burns up due to friction. At whose expense is the heat energy 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 comets velocity in general. Yet the work done by the gravitational force over every complete orbit of the comet is zero. Why?

(c) An artificial satellite orbiting the earth in very thin atmosphere loses its energy gradually due to dissipation against atmospheric resistance, however small. Why then does its speed increase progressively as it comes closer and closer to the earth?

(d) In Figure (i) the man walks

2

m

carrying a mass of

15

k g

on his hands. In Figure (ii), he walks the same distance pulling the rope behind him. The rope goes over a pulley, and a mass of

15

k g

hangs at its other end. In which case is the work done greater?

Answer the following:

(a) The casing of a rocket in flight burns up due to friction. At whose expense is the heat energy 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 gravitational force over every complete orbit of the comet is zero. Why?

(d) In Fig. 6.13(i) the man walks 2 m carrying a mass of 15 kg on his hands. In Fig. 6.13(ii), he walks the same distance pulling the rope behind him. The rope goes over a pulley, and a mass of 15 kg hangs at its other end. In which case is the work done greater?

Fig. 6.13

A meteor burns due to the heat of the earth's atmosphere. Then how is a rocket able to escape this heat while leaving and entering the atmosphere and also it doesn't burn? How

Q. When the fuel in the rocket burns, the rocket moves vertically upward due to :

Q. How does the burning of liquid hydrogen take place in rockets and other space crafts? Does it also require hydrogen to burn? How are they burning outside the atmosphere if the earth?

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