Let’s solve the problem step by step.
We are given a pulley system with 4 wheels (pulleys). The load is 120 pounds. We need to find how much effort (force) is required to lift it.
In a pulley system, the mechanical advantage (MA) tells us how many times the machine multiplies your input force. For an ideal pulley system (ignoring friction), the mechanical advantage equals the number of rope segments supporting the load — which in this case is equal to the number of pulleys if they’re arranged in a standard block-and-tackle setup where each pulley adds one supporting segment.
Looking at the diagram: there are 4 pulleys stacked vertically, and the rope goes up and down through them. In such setups, if the rope is attached to the top fixed pulley and goes down through movable pulleys, the number of rope segments pulling up on the load equals the number of pulleys —
if the last segment is being pulled downward (which it is, since the person is pulling down on the free end).
Actually, let’s count carefully:
- Start from the hook holding the load → that’s connected to the bottom pulley.
- Rope goes up to next pulley → that’s 1 segment.
- Down to next → 2nd segment.
- Up to next → 3rd segment.
- Down to top pulley → 4th segment.
- Then the free end is pulled down — so yes,
4 rope segments are supporting the load.
Therefore, Mechanical Advantage = 4.
Mechanical Advantage (MA) = Load / Effort
So,
Effort = Load / MA
Effort = 120 pounds / 4
Effort = 30 pounds
✔ Double-check: If you have 4 ropes sharing the weight, each carries 1/4 of the load → 120 ÷ 4 = 30. Correct.
Final Answer:
30
Parent Tip: Review the logic above to help your child master the concept of mechanical advantage of simple machines worksheet.
