Zero velocity means zero
Below is a picture of a billiard ball which rolls into a wall and
bounces back. The arrows indicate the direction of motion of the
ball. Students are asked to draw velocity and acceleration vectors
for the ball at each of the following times: before striking the
wall, the instant ball is in contact with the wall, and after
striking the wall. If the acceleration is zero for any or all of
these cases, explicitly state that.
This misconception focuses on the turn
around point, when the ball is contact with the wall. When giving the
velocity and acceleration vectors for the instant that the ball is in
contact with the wall, students who suffer from this misconception
will say that the acceleration must be zero, since the velocity is
zero at that instant.
Related misconceptions/student difficulties that may
arise in the question:
(smaller) velocity means larger (smaller) acceleration.
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