Gravitation NCERT Solutions Class 11 Physics - Solved Exercise Question 8.13

Question 8.13:
How will you ‘weigh the sun’, that is estimate its mass? The mean orbital radius of the earth around the sun is 1.5 × 108 km.
Solution:
Orbital radius of the Earth around the Sun, r = 1.5 × 1011 m
Time taken by the Earth to complete one revolution around the Sun,
T = 1 year = 365.25 days
= 365.25 × 24 × 60 × 60 s
Universal gravitational constant, G = 6.67 × 10–11 Nm2 kg–2
Thus, mass of the Sun can be calculated using the relation,
M = 4π2r3 / GT2
= 4 X 3.142 X (1.5 X 1011)3 / [ 6.67 X 10-11 X (365.25 X 24 X 60 X 60)2]
= 2 X 1030 kg

Hence, the mass of the Sun is 2 × 1030 kg.

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