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Entrance turnstiles are used to control access to train stations and sports stadiums - Leaving Cert Engineering - Question 8 - 2017
Question 8
Entrance turnstiles are used to control access to train stations and sports stadiums. (i) Describe, with the aid of a diagram, a suitable mechanism which allows a t... show full transcript
Worked Solution & Example Answer:Entrance turnstiles are used to control access to train stations and sports stadiums - Leaving Cert Engineering - Question 8 - 2017
Step 1
Describe, with the aid of a diagram, a suitable mechanism which allows a turnstile to rotate in one direction.
Answer
A suitable mechanism for the operation of a turnstile is a ratchet and pawl. This device allows continuous linear or rotary motion in one direction while preventing motion in the opposite direction. Here’s a diagram representing this mechanism:
┌───\
| Pawl
└───/
↓
Ratchet
In this configuration, the pawl engages with the teeth of the ratchet wheel, allowing the turnstile to move freely in one direction as individuals push through, but locks in place when pushed in the reverse direction.
Step 2
Other than a turnstile, identify two applications for the mechanism described by you in Q8(a)(i).
Answer
Two additional applications for the ratchet and pawl mechanism include:
- Clothes line: It allows the line to be pulled out and held taut without reversing.
- Hoists: Commonly used in lifting applications where control on direction is required.
Step 3
Describe a mechanism that transmits motion through 90°.
Answer
A suitable mechanism for transmitting motion through 90° is the bevel gear. Bevel gears are designed to mesh at an angle, allowing the input shaft and output shaft to be oriented at 90 degrees to one another. These gears facilitate the transfer of rotational power in mechanical systems.
Step 4
State two advantages of helical gears over spur gears.
Answer
Two advantages of helical gears over spur gears are:
- Smooth operation: Helical gears engage more gradually than spur gears, leading to less noise and smoother operation.
- Higher load capacity: The staggered teeth provide a larger surface area for load distribution, enhancing the strength and durability of the gear.
Step 5
Outline a suitable use for a cam and follower mechanism.
Answer
A suitable use for a cam and follower mechanism is in internal combustion engines, where the cam operates the valves. As the cam rotates, it pushes the follower, causing the valves to open and close at specific timing intervals relative to the engine cycle.
Step 6
Give two uses for a cylindrical roller bearing.
Answer
Two uses for cylindrical roller bearings include:
- Industrial machinery: Used in applications that require support under heavy radial loads, like conveyor systems.
- Automotive: Commonly found in transmissions and differentials where they handle high loads and reduce friction.
Step 7
Describe the operation of a capacitor.
Answer
A capacitor is an electronic component that stores energy in an electric field. It consists of two conductive plates separated by an insulating material (dielectric). When voltage is applied, charge collects on the plates, allowing the capacitor to store energy which can be released when needed. Capacitors are used in various applications, including filtering, timing circuits, and energy storage.
Step 8
Describe, with the aid of a diagram, a suitable mechanism to allow the sliding door to open.
Answer
A suitable mechanism to operate a sliding door is a toothed belt and pulley system. As the motor rotates, it drives the pulleys attached to the belt, causing the door to slide open.
Pulley
┌───────\
| | ← Door
| | Sliding
| | Mechanism
└───────/
Toothed Belt
This mechanism ensures smooth and efficient operation of the sliding door.
Step 9
Describe, with the aid of a diagram, a mechanism which will allow the ramp to be automated.
Answer
To automate the ramp, a worm and worm wheel drive can be used. This mechanism provides a secure and controlled motion. As the worm turns, it drives the worm wheel, which in turn connects to the ramp mechanism, allowing it to lift or lower as needed.
Worm
┌───────\
| Worm Wheel
| ← Ramp
└───────/
This setup allows precise control over the ramp’s movement and can be integrated with sensors for automatic operation.