FAA Aviation Mechanic General (AMG)Physics, Math and Fluid LinesMedium
A test cart holding an avionics component weighing 64.4 pounds is pushed across a frictionless bench with a horizontal acceleration of 10 ft/sec². What horizontal force is being applied to the cart?
- A20 lb
- B644 lb
- C6.4 lb
- D32.2 lb
Show answer & explanationAnswer & explanation
Correct answer: A. 20 lb
First convert weight to mass in slugs: mass = weight / g = 64.4 / 32.2 = 2 slugs. Then apply Newton's Second Law: F = ma = 2 × 10 = 20 lb.
Why the other options are wrong
- B. This treats weight directly as mass, skipping the conversion to slugs.
- C. This results from dividing weight by acceleration instead of using mass properly.
- D. This is simply the value of gravitational acceleration, not the applied force.
Newton's Second Law (F=ma)
Force equals mass times acceleration; in English units, mass is measured in slugs (weight in pounds divided by 32.2 ft/s²).
- Mass (slugs) = Weight (lb) / 32.2 ft/s²
- Force (lb) = mass (slugs) × acceleration (ft/s²)
- Do not confuse weight (a force) with mass in calculations
Memory trick: 'Slugs push, pounds pull' — always convert weight to mass before F=ma.