Final answer:
A pulley can stop spinning due to zero tension in the string or the presence of friction in the pulley system. An example is the Atwood machine.
Step-by-step explanation:
A pulley can stop spinning due to several reasons. One possible reason is when the tension in the string or rope attached to the pulley becomes zero. When this happens, there is no force acting on the pulley to keep it rotating, causing it to come to a stop. Another reason could be the presence of friction or resistance in the pulley system, which can slow down and eventually stop the pulley from spinning.
An example of a pulley system is the Atwood machine, which consists of a rope running over a pulley with two objects of different masses attached. The weight of the objects creates a tension in the rope, causing the pulley to rotate. However, once the difference in masses becomes zero or the tension in the rope becomes zero, the pulley will stop spinning.
Keywords: pulley, tension, friction, Atwood machine