In an ideal lever, which option correctly describes mechanical advantage?

• A. MA equals the sum of the lever arms
• B. MA equals the ratio of the lengths of the lever arms
• C. MA equals the product of the forces
• D. MA equals the difference between the lever arms

Answer: (B)

Key idea: in an ideal lever, torque must balance, so the input force times its distance from the fulcrum equals the output force times its distance. Because mechanical advantage is the ratio F_out / F_in, you get MA = d_in / d_out, the ratio of the lever arms from the fulcrum. This means a longer input arm compared with the output arm increases the force you can lift (for the same effort), at the cost of moving the input through a larger distance. For example, if the input arm is twice as long as the output arm, MA is 2, so you lift twice the weight with half as much movement. The other options don’t fit because they mix lengths and forces in ways that don’t reflect torque balance or produce a dimensionally correct, unitless ratio.