Question

Find the order of magnitude of the mass of the star, whose radius is $384\times {10}^6$ m and average density is $4\times {10}^3$ kg $m^{-3}$ :

• A. 30
• B. 29
• C. 24
• D. 21

Answer 1

The correct option is A 30

Radius of star $r=384\times {10}^{6}m$

So, Volume of star is $V=4\pi r^3/3=2.371\times {10}^{26}{m}^3$

Density of star is $\rho =4\times {10}^{3}kg{m}^{-3}$

Mass of star is $M=V\times \rho \approx 9.5\times {10}^{29}kg=0.95\times {10}^{30}kg$

So the mass is of order of ${10}^{30}kg$