A ball is fastened to one end of a 30cm string, and the other end is held fixed to a support. the ball whirls in a horizontal circle. Find the speed of the ball in its circular path if the string makes an angle of 30 degrees to the vertical.

Answer 1

string tension T

force up = T cos 30 = .866 T
force horizontal = T sin 30 = .5 T

radius = 0.30 sin 30 = 0.15

so
.5 T = m v^2/r
and
m g = .866 T so T = 1.15 m g

.5 (1.15) m (9.81) = m v^2/.15

v^2 = .846
v = .92 m/s