What will happen if you whirl a rock at the end of a string and it follows a circular path and the string breaks?

If you whirl a rock at the end of a string and it follows a circular path, the rock is experiencing centripetal force directed towards the center of the circle. If the string breaks, the rock will no longer have this inward force acting on it and will continue to move in a straight line tangent to its circular path at the point where the string broke, due to inertia. This is described by Newton's first law of motion, which states that an object in motion will remain in motion in a straight line unless acted upon by an external force.