What is the efficiency of the machine?

Question

A jacks screw has Ideal Mechanical Advantage of 25lb, and a force of 40lb is applied to lift a load of 300lb. What load can be lifted by the machine if it is operated by a force of 60lb?

Answer 1

Ideal mechanical advantage:
IMA = (effort distance) ÷ (resistance distance)
Actual mechanical advantage:
AMA = (actual resistance force) ÷ (effort force)
Efficiency = (Mechanical advantage) ÷ (velocity ratio)
= (Mechanical advantage) ÷ (IMA)

IMA has no units. Notice that the units of force or weight cancel out.

This example:
AMA = 300/40 = 7.5
actual resistance force = (AMA)(effort force) = (7.5)(60) = 450lb
Efficiency:
Efficiency = (Mechanical advantage) ÷ (IMA) = (7.5) ÷ (25) = 30%