# Q5 (a) 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?

The total energy is given by :

$E\ =\ K.E\ +\ P.E$

or                                           $=\ \frac{1}{2}mv^2\ +\ mgh$

The burning of casing results in a reduction in the mass of the rocket. This leads to a lowering in the total energy.

Thus heat required for burning is obtained from the expenses of the rocket.

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