Does anyone know the solution to this problem from Isaac physics?
"Under certain conditions the speed c,c of surface water waves is given by c = (gd)^1/2, where g,g is the gravitational acceleration and d,d is the depth of water (you may assume that this is valid for the whole of this question).
A flat-topped, parallel-sided ridge lies under the surface of a lake. The depth of water at the ridge is d 1, and the depth everywhere else is d 2.
Surface waves are travelling across the ridge (i.e. they are already travelling above the ridge) at an angle θ to the length of the ridge.
Find the minimum value of θ for which the waves will be able to travel past the ridge into the deeper region."