A tetherball is tied to the end of a 2.1-m string of negligible mass. The ball is struck so that it moves in uniform circular motion in a horizontal plane, and the string makes an angle of 26°
with the vertical pole. The mass of the ball is 1.3 kg. What is the tension in the string?

Let t denote the magnitude of the tension in the string and w the weight of the ball. We have

w = (1.3 kg) g = 12.74 N

where g = 9.80 m/s² is the magnitude of the acceleration due to gravity.

In the vertical direction, the ball is in equilibrium, so that, by Newton's second law, we have

t cos(26º) - w = 0

Solving for t gives

t = w sec(26º) ≈ 14 N

365.25 earth days are in the year of a light year