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7.Gravitation
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The mean radius of the earth's orbit round the sun is $1.5 \times 10^{11}.$ The mean radius of the orbit of mercury round the sun is $6 \times10^{10}\,m.$ The mercury will rotate around the sun in
A
A year
B
Nearly $4$ years
C
Nearly $\frac{1}{4}$ year
D
$2.5$ years
Solution
$\frac{T_{1}^{2}}{q_{1}^{3}}=\frac{T_{2}^{2}}{r_{2}^{3}}$
$\frac{1}{\left(1 \cdot 5 \times 10^{11}\right)^{3}}=\frac{T_{2}^{2}}{\left(6 \times 10^{10}\right)^{3}}$
$T_{2}=\sqrt{\left(\frac{6 \times 10^{10}}{1.5 \times 10^{11}}\right)^{3}}$
$=\frac{\sqrt{\left(\frac{4}{10}\right)^{3}}}{\sqrt{\frac{64}{1000}}}$
$=\frac{8}{10 \sqrt{10}}$
$=\frac{0.8}{3.14}$
$\simeq 0.25$
Standard 11
Physics
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