Vectors - NCEA Level 2, year 12?

Question

A model aircraft flies in a circular horizontal path, held in place by a string or length, r. The tension on the string is F newtons when the aircraft flies at v metres per second. It takes one second to complete the circuit.

If the lenght of the srting is maintained at 3r, and the aircraft flies (again) with speed v, the what is the new tension in the string?

Answer 1

F = (mv^2)/r
F2 = (mv^2)/3r
F2/F = 1/3