Q15 of 48 Page 38

A raindrop falling from a height h above ground, attains a near terminal velocity when it has fallen through a height (3/4) h. Which of the diagrams shown in Fig. 6.8 correctly shows the change in kinetic and potential energy of the drop during its fall up to the ground?

we know that at height h, P.E. is maximum and K.E.=0(∵ v=0)

Now, as the raindrop falls its P.E. starts decreasing and K.E.


starts increasing. Hence, total mechanical energy remains


conserved if air resistance is neglected.


If there is some air resistance, then there exists a force called


upthrust. So, as velocity increases upthrust also increases.


∴ during rainfall first its velocity increases then become


constant after sometime. (this velocity is termed as terminal


velocity.) Hence, K.E. also becomes constant and P.E.


decreases continuously as drop is falling continuously.


option (b) represents the correct diagram.

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