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NEET 2019
Exam
NEET
Year
2019
Subject
Physics
Chapter
Oscillations

NEET 2019 · Physics · Oscillations

A mass falls from a height ' h ' and its time of fall ' t ' is...

A mass falls from a height ' hh ' and its time of fall ' tt ' is recorded in terms of time period TT of a simple pendulum. On the surface of earth it is found that t=2 Tt=2 \mathrm{~T}. The entire set uu is taken on the surface of another planet whose mass is half of earth and radius the same. Same experiment is repeated and corresponding times noted as t′\mathrm{t}^{\prime} and T′\mathrm{T}^{\prime}.

Options

  1. At′=2T′t^{\prime}=\sqrt{2} T^{\prime}
  2. Bt′>2T′t^{\prime}>2 T^{\prime}
  3. Ct′<2T′t^{\prime} < 2 T^{\prime}
  4. Dt′=2T′t^{\prime}=2 T^{\prime}

Correct answer

D. t′=2T′t^{\prime}=2 T^{\prime}

Step-by-step solution

The distance covered by the mass falling from height ' hh ' during its time of fall ' tt ' is given by s=h=ut+12gt2 As, u=0⇒h=12gt2⇒t=2 h g\begin{array}{r}\mathrm{s}=\mathrm{h}=\mathrm{ut}+\frac{1}{2} \mathrm{gt}^2 \\ \text{ As, } \mathrm{u}=0 \Rightarrow \mathrm{h}=\frac{1}{2} \mathrm{gt}^2 \Rightarrow \mathrm{t}=\sqrt{\frac{2 \mathrm{~h}}{\mathrm{~g}}} \end{array}The time period of simple pendulum is T=\mathrm{T}=2 πlg\pi \sqrt{\frac{\mathrm{l}}{\mathrm{g}}}where, lis the length of the pendulum. From Eq. (i) and (ii), since ' hh ' and ' ll ' are constant so, we can conclude that, t∝lg and T∝lg∴tT=l\mathrm{t} \propto \frac{\mathrm{l}}{\sqrt{\mathrm{g}}} \text{ and } \mathrm{T} \propto \frac{\mathrm{l}}{\sqrt{\mathrm{g}}} \quad \therefore \frac{\mathrm{t}}{\mathrm{T}}=\mathrm{l}Thus, the ratio of time of fall and time period of pendulum is independent of value of gravity (g)(\mathrm{g}) or any other parameter like mass and radius of the planet. Thus, the relation between \mathrmt′\mathrmt^{\prime} and T′\mathrm{T}^{\prime} on another planet irrespective of its mass or radius will remains same as it was on earth i.e. \mathrmt^{\prime}=2  T′\mathrm{~T}^{\prime}
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