Question

A stone of 400g is whirled by a string of length 2.8m so that it moves in horizontal circle of radius 0.7m.find the tension on the string.

Answer 1

m v^2/r horizontal
m g down

tan theta = mg/(mv^2/R)where theta is angle down from horizontal
but
cos theta = .7/2.8
so theta = 75.5 deg
so tan theta = 3.87
so
3.87 = mg/mv^2/R = 9.81/(v^2/.7)

v = 1.33 m/s

m v^2/R = .4*1.77/.7 = 1.01
m g = .4*9.81 = 3.92

T^2 = 1.01^2 +3.92^2

T = 4.04 N