Question

A 0.50 kg ball that is tied to the end of a 1.4 m light cord is revolved in a horizontal plane with the cord making a 30° angle with the vertical. (b) If the ball is revolved so that its speed is 4.0 m/s, what angle does the cord make with the vertical?

Answer 1

You already said the cord makes a 30 degree angle with the vertical. I don't get it.

A speed of 4.0 m/s requires a certain angle A such that

M V^2/(L sin A) = T sin A
T cos A = M g

so
V^2/(L sinA) = g tanA

Solve for A

Eliminate T