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7.Gravitation
medium
$T$ is the time period of simple pendulum on the earth's surface. Its time period becomes $x T$ when taken to a height $R$ (equal to earth's radius) above the earth's surface. Then, the value of $x$ will be:
A
$4$
B
$2$
C
$\frac{1}{2}$
D
$\frac{1}{4}$
(JEE MAIN-2023)
Solution
At surface of earth time period
$T =2 \pi \sqrt{\frac{\ell}{ g }}$
At height $h = R$
$g ^{\prime}=\frac{ g }{\left(1+\frac{ h }{ R }\right)^2}=\frac{ g }{4}$
$xT =2 \pi \sqrt{\frac{\ell}{( g / 4)}}$
$\Rightarrow xT =2 \times 2 \pi \sqrt{\frac{\ell}{ g }}$
$\Rightarrow xT =2 T \Rightarrow x =2$
Standard 11
Physics