Why Is Tension T=2mg and Not T=mg at Time t=τ?

[user5]

A massless rod of length L attached to mass m and with axle to cart of mass M. The cart has a shape of equilateral triangle (edge L). the cart is at rest and its center of mass is above x=0 and a rod is perpendicular to the ground. the cart is free to move without friction. at time t=0 the mass m is released and starts to fall to the left. at time t=τ the rod is parallel to the ground. Why the tension from the stick at time t=τ is T=mv^2/L=2mg and not T=mv^2/L=mg?

 

[adjacent]

What do you think?
Any relevant equations?
Any ideas of you?

 

[user5]

mv^2/L is the radial force that need to be equated with the tension force...but the torque mgsin 90 = mg