A 160g stone, tied to a thread, swings in a horizontal circle with a 100 cm diameter. if the maximum tension the thread can withstand before snapping is 28 N, find the

A) Maximum speed of the stone
B) Acceleration of the stone at this speed.
I solved A with V= sqrt of rT/m and came up with 12.5 m/s^2. Can someone help or get me in the right direction. Thanks.

I solved B. by a=V^2/r and came up with 312.5 m/s^2. Does this look right?