heavy ball is attached to a string and swung in a circular path in a horizontal
plane as shown in the animation. At the point indicated the string suddenly
breaks at the ball. Four animations represent possible results when the string
breaks at point P.
Which of the four animations properly represents the path of the ball if the
string breaks at point P?
Reference: See Giancoli-PA: 5-1, Giancoli-SE: 3-8.
Animation B, the ball moves tangent to the circle at point P (not shown). This
problem is an excellent warm up for the discussion of uniform circular motion.
Students often have a hard time with the cause of uniform circular motion. Here,
the string is the cause of the ball's acceleration towards the center of the
circle. In fact, without it, there is no longer an acceleration and the ball
continues at a constant velocity which is tangent to the circle at point P.
Students will often laugh at animations such as Animation D, even though they
will answer this question incorrectly (choosing this answer) on the FCI.
Script Author: Melissa Dancy