NEIEP Mechanics Practice Exam

What does doubling the reeve change about a hoist's operation?

1. Increases speed

2. Decreases weight

3. Reduces torque

4. Increases torque and decreases speed

The correct answer is: Increases torque and decreases speed

Doubling the reeve in a hoisting system fundamentally alters how the hoist operates by increasing the torque while decreasing the speed. This occurs because when the reeving is doubled, more rope is added to the system, which distributes the load more evenly and allows for a greater mechanical advantage. As you increase the number of reeves, the force applied on the load (torque) is amplified, making it easier to lift heavier objects with the same amount of applied force. However, this also leads to a reduction in speed since the mechanism must travel a longer distance with each turn of the drum or pulley. Essentially, the trade-off here is that while you can lift heavier items more easily, the lifting process becomes slower due to the increased length of rope that must be moved. This principle can be illustrated by considering the pulley system's mechanical advantage. Each additional reeve introduces a new path for the rope, thereby redistributing the load and allowing for a greater lifting capacity while also necessitating more movement for the same distance of lift, thus reducing speed in the operation.