Ring Gravity (11-14-2020)

Consider a uniform circular ring of mass M M and radius R R . The center of the ring is located 2 2 distance units away from a point particle of mass m m . The particle lies in the same plane as the ring.

What is the magnitude of the gravitational force between them?

Details and Assumptions:
M = 1 kg , R = 1 m , G = 1 N m 2 kg 2 M = 1\text{ kg}, R = 1\text{ m} , G = 1 \text{ N m}^2 \text{ kg}^{-2} .


The answer is 0.3114.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Karan Chatrath
Nov 14, 2020

Take any general point on the ring as r = ( cos t , sin t ) \vec{r} = (\cos{t},\sin{t}) and define the location of the point mass as r p = ( 2 , 0 ) \vec{r}_p = (2,0) . By applying Newton's law of gravity, for an elementary arc of length d t dt in the neighbourhood of r \vec{r} leads to the following. Based on symmetry, only the X component of force would be nonzero. After simplifications, the required integrand for the X force component is also shown in the following step.

d F x = d F i ^ = G ( M d t 2 π ) m ( ( r r p ) i ^ r r p 3 ) F x = 1 2 π 0 2 π ( cos t 2 ) d t ( 5 4 cos t ) 3 / 2 0.311405152555898 dF_x = d\vec{F} \cdot \hat{i} = G\left(\frac{M \ dt}{2\pi} \right)m \left(\frac{(\vec{r}-\vec{r}_p) \cdot \hat{i}}{\lvert \vec{r}-\vec{r}_p \rvert^3}\right) \implies F_x =\frac{1}{2\pi} \int_{0}^{2 \pi}\frac{(\cos{t}-2) \ dt}{(5-4\cos{t})^{3/2}} \approx -0.311405152555898

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...