7.Gravitation
medium

પૃથ્વીની સપાટીથી ..... $km$ ઊંચાઇએ ગુરુત્વીય સ્થિતિમાન અને ગુરુત્વપ્રવેગ $g$ નું મૂલ્ય અનુક્રમે $-5.4 \times 10^{7} \; Jkg^{-1}$  અને $6.0\;ms^{-2} $ છે. પૃથ્વીની ત્રિજયા $ 6400\;km$ છે.

A

$1600$

B

$1400$

C

$2000$

D

$2600$

(NEET-2016)

Solution

             Gravitation potential at a height $h$ from the surface of earth, ${V_h} =  – 5.4 \times {10^7}\,J\,k{g^{ – 1}}$

At the same point acceleration due to gravity,

${g_h}$ $= 6\,ms^{-2}$

$R=6400\, km=6.4\times10^6\,m$

We know, ${V_h} =  – \frac{{GM}}{{\left( {R + h} \right)}}$

${g_h} = \frac{{GM}}{{{{\left( {R + h} \right)}^2}}} =  – \frac{{{V_h}}}{{R + h}} \Rightarrow R + h =  – \frac{{{V_h}}}{{{g_h}}}$

$\therefore \,\,h =  – \frac{{{V_h}}}{{{g_h}}} – R = \frac{{\left( { – 5.4 \times {{10}^7}} \right)}}{6} – 6.4 \times {10^6}$

$ = 9 \times {10^6} – 6.4 \times {10^6} = 2600\,Km$

Standard 11
Physics

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