| Date | May 2012 | Marks available | 1 | Reference code | 12M.1.SL.TZ1.5 |
| Level | Standard level | Paper | Paper 1 | Time zone | Time zone 1 |
| Command term | Question number | 5 | Adapted from | N/A |
Question
A pendulum swings back and forth in a circular arc between X and Y.
The pendulum bob is
A. always in equilibrium.
B. only in equilibrium at X and Y.
C. in equilibrium as it passes through the central position.
D. never in equilibrium.
Markscheme
D
Examiners report
In this question the majority of candidates thought, incorrectly, that the ball would be in equilibrium at the central position when the string is vertical. The ball is obviously not in equilibrium since it is moving on a circular arc and so at the vertical position there must be a net force directed towards the center of the arc and so there cannot be equilibrium.
