Mechanical Aptitude Mechanical Aptitude Knowledge 4 — Questions and Answers
Question 1: A 10 kg object sits on a frictionless inclined plane at 30°. What force parallel to the slope is needed to hold it stationary? (g = 10 m/s²)
- 50 N (Correct answer)
- 86.6 N
- 100 N
- 10 N
Correct answer: 50 N
Force along slope = mg × sin(30°) = 100 × 0.5 = 50 N.
Question 2: Which valve type is best for on/off control with minimal flow restriction when fully open?
- Needle valve
- Globe valve
- Gate valve (Correct answer)
- Check valve
Correct answer: Gate valve
Gate valves have a flat gate that lifts completely out of the flow path, offering very low resistance when fully open.
Question 3: The mechanical advantage of a wheel and axle is calculated as:
- Axle radius ÷ wheel radius
- Wheel radius ÷ axle radius (Correct answer)
- Wheel circumference × force applied
- Axle diameter × RPM
Correct answer: Wheel radius ÷ axle radius
MA = Wheel radius ÷ Axle radius; the larger the wheel compared to the axle, the greater the mechanical advantage.
Question 4: What happens to electrical resistance when the length of a wire is doubled?
- Resistance is halved
- Resistance stays the same
- Resistance doubles (Correct answer)
- Resistance quadruples
Correct answer: Resistance doubles
Resistance is directly proportional to wire length: R = ρL/A, so doubling L doubles R.
Question 5: A centrifugal pump is running but not moving fluid. The most likely cause is:
- Motor is running backwards
- Discharge valve is fully open
- Pump is cavitating due to air in the suction line (Correct answer)
- Fluid viscosity is too low
Correct answer: Pump is cavitating due to air in the suction line
Air entrainment in the suction line prevents the pump from building pressure, causing it to lose prime and stop moving fluid.
Question 6: A bolt is tightened using torque to create clamping force. Lubricating the threads before tightening will:
- Increase friction and reduce clamping force
- Have no effect on clamping force
- Increase clamping force for the same applied torque (Correct answer)
- Reduce the bolt's tensile strength
Correct answer: Increase clamping force for the same applied torque
Lubrication reduces friction losses, so more of the applied torque converts to clamping force (bolt tension).
Question 7: Which simple machine is a hammer claw used to pull nails?
- Wedge
- Screw
- Lever (Correct answer)
- Pulley
Correct answer: Lever
The hammer claw acts as a first-class lever, with the head as the fulcrum to multiply pulling force on the nail.
Mechanical Aptitude Mechanical Aptitude Knowledge 4
A 10 kg object sits on a frictionless inclined plane at 30°.
What force parallel to the slope is needed to hold it stationary? (g = 10 m/s²)