Q99 / 180 · NEET 2019 (All India) · Physics

The work done to raise a mass $m$ from the surface of the earth to a height $h$ , which is equal to the radius of the earth is:

A
$m g R$
B
$2 m g R$
Correct answer
C
$\frac{1}{2} m g R$
D
$\frac{3}{2} m g R$

Solution

W = U_{f} - U_{i}

= \frac{- G M m}{2 R} - (\frac{- G M m}{R})

= \frac{G M m}{2 R}

W = \frac{1}{2} m g R

(∵ \frac{G M}{R^{2}} = g)

Hence, the correct answer is option: 'C'.

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