Question

a 20N attached to the end of a 20m long string is rotating as a conical pendulum. if it rotated as 50 rev/min, what angle will the string make with the vertical?

Answer 1

$$T=2\pi\sqrt{\frac{l\cos\theta}{g}},\\\space\\ \frac{60}{50}=2\pi\sqrt{\frac{20·\cos\theta}{9.8}},\\\space\\ \cos\theta=0.018,\\\space\\ \theta=89°.$$