I have a physics problem that says
A 76.0-kg boulder is rolling horizontally at the top of a vertical cliff that is 20m above the surface of a lake. The top of the vertical face of a dam is located 100m from the foot of the cliff, with the top of the dam level with the surface of the water in the lake. A level plain is 25m below the top of the dam. What must be the minimum speed of the rock just as it leaves the cliff so it will travel to the plain without striking the dam?
I tried to solve the problem using projectile motion formulas. What I did was finding velocity by finding the x and y components. But this problem didn't mention any angle or time, which the formulas required. So I tried to find the travel time of stone but it was not good way to solve this question.
How can I find the minimum speed without using time?