Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

Published by Pearson
ISBN 10: 0321740904
ISBN 13: 978-0-32174-090-8

Chapter 13 - Newton's Theory of Gravity - Exercises and Problems - Page 374: 52

Answer

See the detailed answer below.

Work Step by Step

a) The speed of a point on the equator of the given neutron star is given by $$v=\dfrac{2\pi R_{star}}{T}$$ $$v=\dfrac{2\pi (10\times 10^3)}{1}=\color{red}{\bf 6.28\times 10^4}\;\rm m/s$$ ________________________________________________ b) According to Newton's gravitational law, the free-fall acceleration at the surface of this star is given by $$g_{\rm surface}=\dfrac{GM_{star}}{R^2_{star}}$$ Plugging the known; $$g_{\rm surface}=\dfrac{(6.67\times 10^{-11})(1.99\times 10^{30})}{ (10\times 10^3)^2}=\color{red}{\bf 1.33\times 10^{12}}\;\rm m/s^2$$ ________________________________________________ c) The weight of the 1-kg mass on the surface of our star is given by $$W=mg_{\rm surface}=1(1.33\times 10^{12})$$ $$W=\color{red}{\bf 1.33\times 10^{12}}\;\rm N$$ ________________________________________________ d) To find the number of revolutions per minute, we need first to find the period of one revolution. $$F_{G}=\dfrac{GM_{star} \color{red}{\bf\not}m_{\rm satellite}}{R_{orbit}^2}= \color{red}{\bf\not}m_{\rm satellite}a_r$$ where $R_{orbit}=R_{star}+h$ and $a_r=v^2/R_{orbit}$ $$ \dfrac{GM_{star} }{(R_{star}+h)^2}= \dfrac{v^2}{(R_{star}+h)}$$ where $v=2\pi R_{orbit}/T $ $$ \dfrac{GM_{star} }{(R_{star}+h)^2}= \dfrac{\left(\dfrac{2\pi (R_{star}+h)}{T} \right)^2}{(R_{star}+h)}$$ $$ \dfrac{GM_{star} }{(R_{star}+h)^2}= \dfrac{4\pi^2 (R_{star}+h)^{ \color{red}{\bf\not}2}}{T^2 \color{red}{\bf\not}(R_{star}+h)} $$ Noting that the number of revolutions is given by $N=1/T$ $$N =\dfrac{1}{\sqrt{\dfrac{4\pi^2(R_{star}+h)^3}{GM_{star}}}}$$ Plugging the known; $$N=\dfrac{1}{\sqrt{\dfrac{4\pi^2([10\times 10^3]+1000)^3}{ (6.67\times 10^{-11})(1.99\times 10^{30})}}}$$ $$N=\bf 1589.35\;\rm rev/s=\color{red}{\bf 9.54\times10^4}\;\rm rev/min$$ ________________________________________________ e) According to Kepler's third law; $$T^2=\left[\dfrac{4\pi ^2}{GM}\right]r^3$$ So the radius of a geosynchronous orbit about the neutron star is given by $$r^3=\dfrac{T^2 GM_{star}}{4\pi^2}$$ $$r =\sqrt[3]{\dfrac{T^2 GM_{star}}{4\pi^2}}$$ Plugging the known; $$r =\sqrt[3]{\dfrac{ (1)^2(6.67\times 10^{-11})(1.99\times 10^{30})}{4\pi^2}}$$ $$r=\color{red}{\bf1.498\times 10^6}\;\rm m$$
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.