An office chair has a prewound torsional spring that allows the chair to tilt backward when a sufficiently large force f is applied. When f is small, the stop at point a prevents the chair from tilting backward. What is the purpose of the stop at point a?
1) To prevent the chair from tilting backward
2) To allow the chair to tilt backward
3) To provide stability to the chair
4) To adjust the height of the chair