Final answer:
The stone tied to the string moves in a circular path with uniform speed until the tension in the string exceeds 400 N, at which point the string will break and the stone will fall freely.
Step-by-step explanation:
When a stone of mass 1 kg is tied to a massless string of length 1 m and swung in a circular path with a uniform speed, the tension in the string provides the necessary centripetal force to keep the stone moving in the circular path. However, if the tension exceeds the breaking tension of the string, which is 400 N, the string will break and the stone will fall freely. A stone tied to a string and swung in a circular path does not move in simple harmonic motion because the restoring force is not proportional to the displacement from the equilibrium position. Similarly, the stone does not move with constant velocity in a straight line, as the velocity changes direction continuously due to the centripetal acceleration, even though the magnitude of the speed might be constant.