forces physics problem - Please Help ASAP

Question

A 0.30 kg stone attached to a 0.8 m long string is rotated in a horizontal plane. The string makes an angle of 15° with the horizontal. Determine the speed of the stone.

Answer 1

the vertical component of the centripetal force must balance the force of gravity.  

Radius of circle = 0.8 * cos 15 = 0.773m  centripetal force = mv^2/r.   This is horizontal component of force in string.  Use tan 15 to get vertical component.

Vertical component = mV^2/r * tan 15 = mg;  V^2 = gr/tan 15  V= 5.31