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7.Gravitation
medium
An object is taken to a height above the surface of earth at a distance $\frac{5}{4} R$ from the centre of the earth. Where radius of earth, $R=6400\,km$. The percentage decrease in the weight of the object will be $....\%$
A
$36$
B
$50$
C
$64$
D
$25$
(JEE MAIN-2022)
Solution

$g _{\text {eff }}=\frac{ g }{\left(1+\frac{ h }{ R }\right)^{2}} ; g _{ eff }=\frac{ g }{\left(1+\frac{1}{4}\right)^{2}}=\frac{16\,g }{25}$
$\text { change }=\frac{g_{\text {off }}-g}{g} \times 100=\frac{\frac{16}{25}-1}{1} \times 100$
$=\frac{-9}{25} \times 100=-36 \%$
Hence $\%$ decrease in the weight $=36 \%$
Standard 11
Physics