If a 175 lb load is lifted with a fixed pulley, what input force is required (neglecting friction)?

If a 175 lb load is lifted with a fixed pulley, what input force is required (neglecting friction)?

• A. 150 lb
• B. 175 lb
• C. 350 lb
• D. 87.5 lb

Answer: (B)

This tests that a fixed pulley does not provide mechanical advantage; it only changes the direction of the force. In a frictionless system with a fixed pulley, the rope tension must balance the weight, so the input force equals the load. Lift a 175 lb load by applying 175 lb of input force. The other numbers would imply some mechanical advantage or additional friction, which a fixed, frictionless pulley does not provide.

This tests that a fixed pulley does not provide mechanical advantage; it only changes the direction of the force. In a frictionless system with a fixed pulley, the rope tension must balance the weight, so the input force equals the load. Lift a 175 lb load by applying 175 lb of input force. The other numbers would imply some mechanical advantage or additional friction, which a fixed, frictionless pulley does not provide.