Firefighter Practice Exam

What happens to the speed of a pulley if the circumference decreases while the other remains constant at a set rpm?

1. It increases

2. It decreases

3. It remains the same

4. It doubles

The correct answer is: It decreases

When the circumference of a pulley decreases while the other pulley remains constant at a set RPM, the speed of the pulley is affected due to the relationship between linear speed and circumference. In a pulley system, the linear speed of the edge of the pulley is determined by the formula: \[ \text{Linear Speed} = \text{RPM} \times \text{Circumference} \] If one pulley has a reduced circumference while maintaining the same rotational speed (RPM), it will cover less distance per rotation. As a result, the linear speed decreases. The force exerted by the pulley is related to its circumference because a smaller circumference means that with each rotation, it effectively moves a shorter distance compared to a larger circumference at the same rate of revolutions. Thus, the correct response highlights that when the circumference is smaller, the linear speed must decrease as long as the RPM remains constant.