EIAT Mechanical Comprehension 5 โ Questions and Answers
Question 1: Work is calculated as:
- Mass ร acceleration
- Force ร distance (Correct answer)
- Force รท area
- Velocity ร time
Correct answer: Force ร distance
Work (W) = Force (F) ร Distance (d); it measures the energy transferred when a force moves an object over a distance.
Question 2: A cam mechanism is used to convert:
- Linear motion into hydraulic pressure
- Rotary motion into reciprocating linear motion (Correct answer)
- Electrical energy into mechanical torque
- Speed into torque through gear reduction
Correct answer: Rotary motion into reciprocating linear motion
A cam converts the continuous rotational motion of a shaft into back-and-forth (reciprocating) linear motion of a follower.
Question 3: In a traction elevator, rope grip is maintained by:
- Magnetic clamping of the sheave
- Friction between the rope and sheave grooves (Correct answer)
- Hydraulic pressure applied to rope clamps
- Mechanical locking pins through each rope
Correct answer: Friction between the rope and sheave grooves
Traction drive relies on friction in the grooved sheave โ rope tension and groove geometry (undercut or round) generate the tractive force.
Question 4: What effect does doubling the diameter of a pipe have on its cross-sectional area?
- Doubles the area
- Triples the area
- Quadruples the area (Correct answer)
- Has no effect on area
Correct answer: Quadruples the area
Area = ฯ(d/2)ยฒ; doubling d gives ฯ(d)ยฒ which is 4 times the original area, so flow capacity increases four-fold.
Question 5: An elevator cab weighs 3,000 lb and is lifted 40 feet in 20 seconds. The power required (ignoring losses) is approximately:
- 600 ft-lb/s (1.09 HP)
- 3,000 ft-lb/s (5.45 HP)
- 6,000 ft-lb/s (10.9 HP) (Correct answer)
- 120,000 ft-lb/s (218 HP)
Correct answer: 6,000 ft-lb/s (10.9 HP)
Power = Work/Time = (3,000 lb ร 40 ft) / 20 s = 6,000 ft-lb/s; dividing by 550 gives ~10.9 HP.
Question 6: A worm gear drive is considered self-locking when the:
- Number of worm starts equals the number of gear teeth
- Lead angle of the worm is less than the friction angle (Correct answer)
- Gear ratio is greater than 20:1
- Lubricant viscosity exceeds 100 cSt
Correct answer: Lead angle of the worm is less than the friction angle
Self-locking occurs when the worm's lead angle is smaller than the friction angle, preventing back-driving from the gear side.
Question 7: The purpose of a compensation rope or chain in a high-rise elevator is to:
- Connect the cab to the emergency brake
- Balance the weight of the long hoisting ropes that shifts as the cab travels (Correct answer)
- Carry electrical power to the cab lighting
- Link the governor to the safety gear
Correct answer: Balance the weight of the long hoisting ropes that shifts as the cab travels
As the cab rises, hoisting rope weight shifts to the counterweight side; compensation ropes hanging below the cab and counterweight rebalance this weight difference.
