Answer:
[tex]T_b=m(g+\frac{v_b^2}{R})[/tex]
Explanation:
At the bottom the tension would be upwards and the weight downwards, their difference being the centripetal force. Taking the upwards direction as positive we then have:
[tex]T_b-mg=F_{cp}=ma_{cp}=m\frac{v_b^2}{R}[/tex]
where we have used the equation for centripetal acceleration. Thus we have:
[tex]T_b=m(g+\frac{v_b^2}{R})[/tex]