Question

A model airplane is flying in a circular loop in the vertical plane, with a radius of 80.0 m. What is the minimum speed that the airplane can maintain without being forced out of the loop?

Answer 1

$$F_g=F_c,$$ $$mg=\dfrac{mv^2}{R},$$ $$v=\sqrt{gR}=\sqrt{9.8\ \dfrac{m}{s^2}\cdot80.0\ m}=28\ \dfrac{m}{s}.$$