SIFT Mechanical Comprehension Questions and Answers 2 — Questions and Answers
Question 1: If a lever has a 4-foot effort arm and a 1-foot resistance arm, what is the mechanical advantage?
- 0.25
- 1
- 4 (Correct answer)
- 5
Correct answer: 4
Mechanical advantage of a lever = effort arm length / resistance arm length = 4 / 1 = 4. A force applied at 4 feet can lift 4 times the load at 1 foot.
The lever is a simple machine that multiplies force. Mechanical Advantage (MA) = Length of effort arm / Length of resistance arm. With MA = 4, you need only 25 pounds of input force to lift 100 pounds of load. The tradeoff is that you must move the effort arm 4 times as far as the load moves.
Question 2: A gear with 10 teeth drives a gear with 40 teeth. What is the gear ratio and what happens to speed?
- Gear ratio 4:1; the driven gear spins 4 times faster
- Gear ratio 1:4; the driven gear spins 4 times slower (Correct answer)
- Gear ratio 4:1; speed stays the same but torque increases
- Gear ratio 1:1; both gears spin at the same speed
Correct answer: Gear ratio 1:4; the driven gear spins 4 times slower
Gear ratio = teeth on driven gear / teeth on driving gear = 40/10 = 4:1, so the driven gear rotates at 1/4 the speed of the driver, but torque is multiplied by 4.
When a small gear drives a larger gear, rotational speed decreases and torque increases proportionally. Here the 40-tooth gear turns at 1/4 the speed of the 10-tooth gear. Torque is multiplied by 4. This is used in transmissions to trade speed for torque or vice versa.
Question 3: Which type of pulley system provides a mechanical advantage of 2?
- A single fixed pulley
- A single movable pulley (Correct answer)
- A block and tackle with three pulleys
- A differential pulley system
Correct answer: A single movable pulley
A single movable pulley provides a mechanical advantage of 2 because the load is supported by two rope segments, halving the effort required.
A fixed pulley only changes the direction of force (MA=1). A movable pulley attaches to the load itself, so two rope segments support the weight. This means you need only half the force to lift the same load, but you must pull twice as much rope — consistent with the law of conservation of energy.
Question 4: What is the relationship between pressure and volume in a gas at constant temperature (Boyle's Law)?
- Pressure and volume are directly proportional — both increase together
- Pressure and volume are inversely proportional — as one increases, the other decreases (Correct answer)
- Pressure and volume are independent — they don't affect each other
- Pressure stays constant regardless of volume changes
Correct answer: Pressure and volume are inversely proportional — as one increases, the other decreases
Boyle's Law states that at constant temperature, the pressure of a gas is inversely proportional to its volume (P₁V₁ = P₂V₂). Compress a gas and its pressure rises.
If you halve the volume of a gas at constant temperature, the pressure doubles. This is why a pump gets harder to push as you compress air into a tire. In engines, the compression stroke reduces cylinder volume dramatically, raising gas pressure and temperature before ignition.
Question 5: A hydraulic system has a small piston with area 2 in² and a large piston with area 20 in². What force does the large piston exert when 10 lbs is applied to the small piston?
- 1 lb
- 10 lb
- 100 lb (Correct answer)
- 200 lb
Correct answer: 100 lb
By Pascal's Principle, pressure is transmitted equally. P = F/A = 10/2 = 5 psi. Force on large piston = P × A = 5 × 20 = 100 lb.
Hydraulic systems multiply force using Pascal's Principle: pressure applied to a confined fluid is transmitted equally in all directions. The larger piston has 10 times the area, so it exerts 10 times the force. This is the principle behind hydraulic brakes, jacks, and aircraft control systems.
Question 6: What is the purpose of a torque wrench?
- To apply unlimited force to a fastener
- To measure and limit the rotational force applied to a fastener to a specified value (Correct answer)
- To remove rounded or damaged bolt heads
- To measure the distance a bolt protrudes through a surface
Correct answer: To measure and limit the rotational force applied to a fastener to a specified value
A torque wrench measures and limits the rotational force (torque) applied to a fastener, ensuring it is tightened to the manufacturer's specified value — not too loose or too tight.
Over-tightening can strip threads or break bolts; under-tightening can cause fasteners to loosen under vibration. Torque specifications in maintenance manuals must be followed precisely, especially in aircraft and engine assembly. Torque wrenches click, slip, or indicate when the set torque value is reached.
SIFT Mechanical Comprehension Questions and Answers 2
If a lever has a 4-foot effort arm and a 1-foot resistance arm, what is the mechanical advantage?