Plant Operator Selection System Test Plant Operator Selection System Physics Principles 4 — Questions and Answers
Question 1: Water at the bottom of a 30-foot tank exerts how much hydrostatic pressure (in psi)?
- 6.5 psi
- 13.0 psi (Correct answer)
- 17.3 psi
- 30.0 psi
Correct answer: 13.0 psi
Pressure = height × 0.433 psi/ft = 30 × 0.433 ≈ 13.0 psi.
Question 2: A machine does 2,000 ft-lb of work in 10 seconds. What is its power output?
- 0.2 hp
- 0.36 hp (Correct answer)
- 3.6 hp
- 36 hp
Correct answer: 0.36 hp
Power = 2000 ft-lb ÷ 10 s = 200 ft-lb/s; 1 hp = 550 ft-lb/s, so 200/550 ≈ 0.36 hp.
Question 3: When a safety relief valve opens on a boiler, it is primarily protecting against:
- Low water level
- Excessive pressure (Correct answer)
- High temperature only
- Feedwater contamination
Correct answer: Excessive pressure
Relief valves are set to open at a maximum allowable working pressure to prevent catastrophic overpressure failure.
Question 4: Which of the following is a correct statement about centrifugal pumps?
- Flow rate decreases as impeller speed increases
- Head developed increases with impeller diameter (Correct answer)
- They are best suited for high-viscosity sludge at low flow
- Priming is never required because they are self-priming by design
Correct answer: Head developed increases with impeller diameter
According to affinity laws, head varies with the square of impeller speed and directly with impeller diameter increase.
Question 5: A 120-volt circuit draws 15 amps. What is the resistance of the load?
- 4 ohms
- 8 ohms (Correct answer)
- 12 ohms
- 1800 ohms
Correct answer: 8 ohms
Ohm's Law: R = V ÷ I = 120 V ÷ 15 A = 8 ohms.
Question 6: Which statement best describes the relationship between temperature and pressure for a gas in a sealed rigid container (constant volume)?
- Pressure is inversely proportional to temperature
- Pressure increases proportionally with absolute temperature (Correct answer)
- Temperature has no effect on pressure in a sealed container
- Pressure decreases as temperature increases
Correct answer: Pressure increases proportionally with absolute temperature
Gay-Lussac's Law states P/T = constant, so pressure increases proportionally with absolute temperature at constant volume.
Question 7: A 5-lb object falls freely from rest. After 2 seconds, what is its approximate velocity?
- 10 ft/s
- 32 ft/s
- 64 ft/s (Correct answer)
- 160 ft/s
Correct answer: 64 ft/s
v = g × t = 32.2 ft/s² × 2 s ≈ 64 ft/s; the object's weight does not affect free-fall acceleration.
Plant Operator Selection System Test Plant Operator Selection System Physics Principles 4
Water at the bottom of a 30-foot tank exerts how much hydrostatic pressure (in psi)?