Answer:
[tex]{K.E = \dfrac{1}{2} mgR[/tex]
Explanation:
For loop-the-loop, to stay at the top of the loop the centripetal force must equal the gravitational force
[tex]mg = \dfrac{mv^2}{R}[/tex]
solving for velocity we get:
[tex]v = \sqrt{gR}[/tex]
Thus, the minimum kinetic energy required is
[tex]K.E = \dfrac{1}{2} mv^2[/tex]
[tex]\boxed{K.E = \dfrac{1}{2} mgR}[/tex]