A Ferris wheel with diameter 110 metres rotates at a constant speed. The lowest point on the wheel is 10 metres above the ground, as shown on the following diagram. P is a point on the wheel. The wheel starts moving with P at the lowest point and completes one revolution in 20 minutes.
The height, h metres, of P above the ground after t minutes is given by h(t)=acos(bt)+c, where a,b,c∈R.
Find the values of a, b and c.