What does 'input force' refer to?

• A. Mechanical advantage of a system
• B. Amount of pull at the running end of the rope
• C. Weight of the anchor
• D. Number of pulleys in the system

Answer: (B)

Input force is the effort you apply to the rope, at the running end, to make the system move. It’s the actual pull you exert to lift or lower the load. In a pulley system, the number of pulleys and the arrangement determine how much load you can move per amount of input, but the input force itself is simply the pull you apply.

Why this fits the choice: the amount of pull at the running end of the rope is exactly the force you exert to drive the system. The other options aren’t the input force: mechanical advantage is the ratio of output to input, not the force you apply; the weight of the anchor is the load, not the input; and the number of pulleys affects potential advantage but isn’t the input force itself.