A girl attaches a rock to a string, which she then swings counter-clockwise in a horizontal circle. The string breaks at point P in the figure, which shows a bird's-eye view (as seen from above). Which path (A-D) will the rock follow?
Correct answer: B. Path B
- A. Path A
- B. Path B
- C. Path C
- D. Path D
Explanation
Along the tangent. When the string breaks, the rock will continue to move in a straight line tangent to the circle at the point where the string broke. This is because of the conservation of momentum. At the point where the string breaks, the rock is moving in a circular path due to the tension in the string. When the string breaks, there is no longer any force acting on the rock to keep it moving in a circular path. However, the rock still has the momentum it had when it was moving in a circle, and this momentum causes it to continue moving in a straight line tangent to the circle. The direction of the tangent is determined by the direction of the rock's velocity at the point where the string broke.
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