Mechanical Engineering Quiz
Questions: 16 · 10 minutes
1. A metal shaft experiences many cycles of alternating stress, each below the material's yield strength. Why might it still fail over time?
Repeated loading can initiate and grow a fatigue crack.
Elastic loading instantly removes the material's tensile strength.
Yield strength applies only when a component is not moving.
Any stress below yield permanently increases the shaft's diameter.
2. Under ideal fan-law assumptions, a fan's rotational speed increases by 10% without changing its geometry. Approximately how much does its volumetric airflow increase?
About 10%
About 21%
About 33%
It remains unchanged because fan size is unchanged.
3. A thermostat uses a small deadband between its heating-on and heating-off temperatures. What is the main operational benefit?
It guarantees identical temperatures in every room.
It reduces rapid cycling when temperature fluctuates near the setpoint.
It removes the need to size the heating equipment.
It keeps the heating system continuously energized.
4. A long steel heating pipe becomes noticeably longer as its operating temperature rises. What is the primary purpose of adding an expansion loop?
To accommodate thermal movement without excessive stress on the pipe and supports
To raise the pipe's allowable internal pressure
To prevent galvanic corrosion between steel components
To keep the flow laminar as the water temperature changes
5. For a rigid body to remain in static equilibrium, which condition must be satisfied?
The center of mass must coincide with the geometric center.
The sum of forces must equal the body's weight, while moments may be nonzero.
Only the horizontal and vertical forces must cancel; moments do not affect equilibrium.
The sums of all forces and all moments must each equal zero.
6. A rooftop unit begins vibrating strongly only when a rotating component reaches a particular speed. Which explanation is most likely?
The component's mass becomes zero at that speed.
Static equilibrium prevents the supports from carrying the load.
The material's thermal conductivity suddenly increases.
The forcing frequency is near a natural frequency, producing resonance.
7. Indoor air has a dew-point temperature of 16°C and passes over an uninsulated pipe whose surface is at 12°C. What should a designer expect?
The air cannot exchange heat with the pipe because it is above freezing.
Moisture will tend to condense on the pipe surface.
The pipe will heat the air until relative humidity reaches zero.
Water on the pipe can only come from a plumbing leak.
8. A balancing valve in a hydronic circuit is partially closed while pump speed remains fixed. What usually happens to the operating point?
System resistance decreases and flow increases.
The pump curve becomes flat, so flow cannot change.
Both pressure and flow fall to zero immediately.
System resistance increases and the operating flow decreases.
9. For a cooling machine, the coefficient of performance is defined as which ratio?
Compressor work input divided by heat rejected
Heat rejected divided by heat removed from the cooled space
Heat removed from the cooled space divided by work input
Heat removed from the cooled space divided by heat rejected
10. Airflow through a duct remains steady while the duct's cross-sectional area is reduced to half its original value. Assuming density is approximately constant, what happens to average air velocity?
It remains unchanged.
It falls to half its original value.
It doubles.
It increases to four times its original value.
11. Why can a counterflow heat exchanger often transfer heat more effectively than a comparable parallel-flow exchanger?
Counterflow prevents either fluid from changing temperature.
Counterflow eliminates all pressure loss through the exchanger.
Counterflow can maintain a larger average temperature difference along the exchanger.
Counterflow makes the thermal conductivity of the wall irrelevant.
12. What is the primary function of a fire damper where a ventilation duct penetrates a fire-resistance-rated barrier?
To regulate normal room temperature by varying airflow
To close under specified fire conditions and limit fire spread through the duct opening
To prevent ordinary fan noise from entering the occupied space
To remove smoke by increasing the duct's airflow in every fire scenario
13. A finite-element model shows a sharp rise in local stress beside a small notch in a loaded bracket. Which principle best explains this result?
Saint-Venant's principle eliminates stress near geometric changes.
Uniform strain causes every point in the bracket to carry the same stress.
The notch acts as a stress concentration.
The notch raises the material's yield strength locally.
14. A pump cavitates because its long, undersized suction line creates excessive pressure loss. Which change most directly addresses the cause?
Throttle the suction valve to stabilize the inlet flow
Increase the suction-pipe diameter or shorten its route
Increase the pump speed to move liquid through the restriction faster
Reduce the suction-pipe diameter to maintain higher velocity
15. The vapor-retarding jacket on insulation around a chilled-water pipe is damaged. Why can this become a moisture problem?
Water vapor can enter the insulation and condense near the cold pipe surface.
The pipe's internal water pressure forces water vapor through the metal wall.
The damage prevents any heat from passing through the insulation.
The exposed insulation immediately causes galvanic corrosion inside the pipe.
16. A simply supported beam carries a single downward point load at the center of its span. Where is the bending moment greatest?
It is uniform along the entire beam.
At both supports
At the quarter-span points only
At the center of the span