First slide

Gravitaional potential energy

Question

A small body is projected from the earth’s surface vertically up with the escape velocity on the earth.Out of the following curves the one that represents the variation of KE with altitude h is

Moderate

A
B
C
D

Solution

Since the body is projected with escape velocity , its total energy is zero.
Now KE + PE = T.E.
$\large \Rightarrow KE+(-\frac{GMm}{R+h})=0\\\\ \Rightarrow KE=\frac{GMm}{(R+h)}\\\\\;At\;h=0,KE=\frac{GMm}{R}\\\\ \;As\;h\rightarrow \alpha , KE\rightarrow 0$
So , option - (4) is right.

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