FUNCTIONAL ANATOMY & BIOMECHANICS · FOUNDATIONS PRACTICE · CHAPTERS 1–2
Can You Reason Through Force and Lever Problems?
How to use: Choose an option, then tap it once to reveal the reasoning. Nothing is scored or stored. If you miss a question, read why the better option fits before moving on.
Three questions worth understanding before you move on to regional mechanics. Draw the axis, decide which distance actually matters, and then check the reasoning.
1. A 15 N force is applied 0.30 m from a fixed axis at 30° to the lever. What is the torque magnitude in the simplified plane?
A. 4.5 N·m
Revisit your choice
That would be the result for a force perpendicular to the lever (90°). At 30°, the perpendicular component is smaller.
Best answer: B. 2.25 N·m
Take it with you: Write the angle and the line of action before reaching for the calculator.
B. 2.25 N·m
Best answer
Correct. τ = 15 N × 0.30 m × sin(30°) = 2.25 N·m.
Take it with you: Write the angle and the line of action before reaching for the calculator.
C. 0.45 N·m
Revisit your choice
The units and geometry do not support that calculation. Check the distance in meters and apply sin(30°).
Best answer: B. 2.25 N·m
Take it with you: Write the angle and the line of action before reaching for the calculator.
2. Why can a third-class lever require more effort force than the external resistance in the ideal static model?
A. The effort arm is usually shorter than the resistance arm.
Best answer
Correct. A short effort moment arm requires more force to balance the same resistance moment, while offering movement-distance and speed advantages.
Take it with you: Lever class is defined by relative axis, effort and resistance positions—not by the diagnosis.
B. The resistance arm is always shorter than the effort arm.
Revisit your choice
That describes a force-advantage geometry, not the ordinary third-class lever setup.
Best answer: A. The effort arm is usually shorter than the resistance arm.
Take it with you: Lever class is defined by relative axis, effort and resistance positions—not by the diagnosis.
C. Mechanical advantage equals the weight held in the hand.
Revisit your choice
No. Mechanical advantage is a ratio relating force or moment arms, not a mass or force measured on its own.
Best answer: A. The effort arm is usually shorter than the resistance arm.
Take it with you: Lever class is defined by relative axis, effort and resistance positions—not by the diagnosis.
3. Two perpendicular external moments act about the same axis: 30 N at 0.20 m and 20 N at 0.30 m. Which has the greater torque magnitude?
A. The 30 N force, because force alone determines torque.
Revisit your choice
Not when the moment arms differ. Multiplying force by perpendicular distance is essential.
Best answer: C. They are equal at 6 N·m each.
Take it with you: Equal external moments do not automatically imply identical internal muscle forces.
B. The 20 N force, because it acts farther away.
Revisit your choice
Distance alone isn’t enough; the smaller force compensates for the longer moment arm.
Best answer: C. They are equal at 6 N·m each.
Take it with you: Equal external moments do not automatically imply identical internal muscle forces.
C. They are equal at 6 N·m each.
Best answer
Correct. 30 × 0.20 = 20 × 0.30 = 6 N·m. The actual muscle forces needed in a body may still differ.
Take it with you: Equal external moments do not automatically imply identical internal muscle forces.
Where to go next
Review why torque is created by a force acting at a perpendicular moment arm and how third-class levers trade force advantage for movement.
Original questions built from FABIO Principles.pdf and FABio Sample Calculation Problems.pdf. These are new teaching numbers, not copies of the class exam or a patient’s individualized exercise plan.
From My PT School Notes · Original student concept checks. Answers are not collected or scored.
