OAR OAR Mechanical Reasoning 4 — Questions and Answers
Question 1: A boat floats because the buoyant force equals its weight. If cargo is added until the boat sinks lower in the water, the buoyant force:
- Decreases as the boat sinks lower
- Remains the same regardless of depth
- Increases as more water is displaced (Correct answer)
- Becomes zero below the waterline
Correct answer: Increases as more water is displaced
Buoyant force equals the weight of displaced water, which increases as the boat sinks deeper.
Question 2: A screw with 20 threads per inch is turned 5 full rotations. How far does it advance into the material?
- 1/4 inch (Correct answer)
- 4 inches
- 20 inches
- 100 inches
Correct answer: 1/4 inch
Each rotation advances the screw 1/20 inch; 5 rotations × (1/20 in) = 1/4 inch.
Question 3: A refrigerator removes heat from inside by using a refrigerant. The compressor's role in this cycle is to:
- Cool the refrigerant by expanding it rapidly
- Pressurize the refrigerant so it can release heat outside (Correct answer)
- Absorb heat directly from the food compartment
- Convert electrical energy into cold air
Correct answer: Pressurize the refrigerant so it can release heat outside
The compressor raises refrigerant pressure, causing it to condense and release absorbed heat at the condenser coils outside.
Question 4: A 60 kg person stands on a scale in an elevator accelerating upward at 2 m/s². What does the scale read? (g = 10 m/s²)
- 480 N
- 600 N
- 720 N (Correct answer)
- 840 N
Correct answer: 720 N
Scale reads N = m(g + a) = 60 × (10 + 2) = 720 N.
Question 5: Three resistors of 6 Ω each are connected in parallel. What is the total resistance of the circuit?
- 0.5 Ω
- 2 Ω (Correct answer)
- 6 Ω
- 18 Ω
Correct answer: 2 Ω
For N equal resistors in parallel: R_total = R/N = 6/3 = 2 Ω.
Question 6: A wheel and axle system has a wheel radius of 30 cm and an axle radius of 5 cm. What mechanical advantage does it provide?
- 1/6
- 1
- 6 (Correct answer)
- 150
Correct answer: 6
Mechanical advantage = wheel radius / axle radius = 30/5 = 6.
Question 7: When a gas in a sealed container is heated at constant volume, its pressure:
- Decreases proportionally
- Stays the same
- Increases proportionally (Correct answer)
- First increases then decreases
Correct answer: Increases proportionally
Gay-Lussac's Law: at constant volume, pressure is directly proportional to absolute temperature.
OAR OAR Mechanical Reasoning 4
A boat floats because the buoyant force equals its weight.
If cargo is added until the boat sinks lower in the water, the buoyant force: