Question

A simple pendulum has a bob of mass M. The bob is on a light string of length l. The string is fixed at C. At position A, the string if horizontal and the bob is at rest. The bob is released from A and swings to B, where the string is vertical. The tension in the string when the bob first reaches B is?

So to find tension I know that F(total) = Tension - (some other force), but I don't know for sure if that force is centripetal force or what.
To set up originally I chose Mg and know it is incorrect so I'm thinking that it is actually none of the above by using conservation of energy and knowing that centripetal force is mv^2/r where r in this case is l and v^2 is 2gh using conservation of energy where
mgh = 1/2mv^2
and then from there getting the formula. So the actual answer would be
m*2*g*h/l

does this sound correct?

Answer 1

Oh wait I think I figured it out from a video.

Total force is equal to mass time centripetal acceleration
Total-F(c) = m*a(c)
Where Total-F(c) = m* v^2/r
T - mg = m * v^2/r

where v^2 = 2gh and h = l and r = l
so you get
T-mg = m * (2*g*l)/l

from that you get

T-mg = 2mg
then finally
T = 3mg

Answer 2

I have no word about your helping me such a way
Thank you