Question

challenge me!
what determines how much rope you need to pull?
how much of the weight of the boxes is supported by the steel girder to which the block & tackle is attached?
make a pulley system that requires the least effort from the worker to lift a box with weight 3w. how much work does he do lifting the boxes a distance d?

Explanation:

1. For the first question: The length of rope pulled depends on the mechanical advantage (number of supporting rope segments) of the block and tackle and the distance the load is lifted. More supporting segments mean more rope must be pulled to move the load the same distance.
2. For the second question: The steel girder supports the total weight of the boxes plus the weight of the block and tackle system itself, as the girter bears the full downward force from the suspended load and pulley hardware.
3. For the third question: To minimize effort, use a pulley system with 3 supporting rope segments (mechanical advantage = 3), so effort force is $W$. Work done is force multiplied by distance; the worker pulls rope a distance $3D$, so work equals $W \times 3D = 3WD$, which matches the work done on the load ($3W \times D$), as pulleys do not reduce total work, only force.

Answer:

1. The number of supporting rope segments (mechanical advantage) of the block and tackle, and the distance the load is lifted, determine how much rope you need to pull.
2. The steel girder supports the full total weight of the boxes plus the weight of the block and tackle system.
3. Use a pulley system with 3 vertical supporting rope segments for the load. The work done by the worker is $3WD$.