Question: The model airplane in the figure below has a mass of 0.80 kg and moves at a constant speed on a circle that is parallel to the ground. Assume that there is no upward lift on the plane generated by its wings. Without such lift, the guideline slopes downward due to the weight of the plane. Find the tension T in the guideline (length = 18 m), for purposes of significant figures, use 0.800 kg for the mass of the plane, 18.0 m for the length of the guideline, and s1 = 18.0 and s2 = 41.0 m/s for the speeds. This is a practice question and the answers are given.
Tension for s1: 17.8 N
Tension for s2: 75.5 N

Please tell me the equation/method used to achieve these answers.