Q100 / 100 · BITSAT 2024 (Memory Based Paper 1) · Physics

A simple pendulum doing small oscillations at a place R height above earth surface has time period of $T_1=4 \mathrm{~s}$. $T_2$ would be it's time period if it is brought to a point which is at a height $2 R$ from earth surface. Choose the correct relation $[\mathrm{R}=$ radius of Earth $]:$

  • A
    $T_1=T_2$
  • B
    $2 \mathrm{~T}_1=3 \mathrm{~T}_2$
  • Correct answer
    C
    $3 \mathrm{~T}_1=2 \mathrm{~T}_2$
  • D
    $2 \mathrm{~T}_1=\mathrm{T}_2$

Solution

Time period of simple pendulum, $\mathrm{T}=2 \pi \sqrt{\frac{l}{\mathrm{~g}}} \& \mathrm{~g}=\frac{\mathrm{GM}}{(\mathrm{R}+\mathrm{h})^2}$ $\therefore \mathrm{T} \propto(\mathrm{R}+\mathrm{h})$ $\Rightarrow \frac{\mathrm{T}_1}{\mathrm{~T}_2}=\frac{\left(\mathrm{R}+\mathrm{h}_1\right)}{\left(\mathrm{R}+\mathrm{h}_2\right)}=\frac{(\mathrm{R}+\mathrm{R})}{(\mathrm{R}+2 \mathrm{R})}=\frac{2}{3} \Rightarrow 3 \mathrm{~T}_1=2 \mathrm{~T}_2$

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

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