Free DAA Mechanical Comprehension: Gears and Cogs Questions and Answers — Questions and Answers
Question 1: If Gear A turns clockwise and is meshed directly with Gear B, which way will Gear B turn?
- Clockwise
- Counter-clockwise (Correct answer)
- It will not turn
- In the same direction as Gear A
Correct answer: Counter-clockwise
When two external gears are meshed directly, they always rotate in opposite directions. Therefore, if Gear A turns clockwise, Gear B must turn counter-clockwise.
Question 2: A driver gear has 10 teeth and the driven gear has 40 teeth. What is the gear ratio?
- 1:4
- 1:1
- 4:1 (Correct answer)
- 10:40
Correct answer: 4:1
The gear ratio is calculated as the number of teeth on the driven gear divided by the number of teeth on the driver gear. In this case, it is 40 / 10 = 4. This is expressed as a ratio of 4:1.
Question 3: If a small gear drives a large gear, what is the effect on the output speed and torque of the large gear?
- Speed increases, torque decreases
- Speed decreases, torque increases (Correct answer)
- Speed and torque both increase
- Speed and torque both decrease
Correct answer: Speed decreases, torque increases
When a small gear (high speed, low torque) drives a large gear, the large gear will rotate more slowly but with greater torque. This setup is used to decrease speed and increase turning force.
Question 4: In a gear train, Gear A (driver) turns clockwise. It meshes with Gear B, which in turn meshes with Gear C. What direction does Gear C turn?
- Clockwise (Correct answer)
- Counter-clockwise
- It depends on the gear size
- It will not turn
Correct answer: Clockwise
Gear A (clockwise) turns Gear B (counter-clockwise). Gear B (counter-clockwise) then turns Gear C (clockwise). Gear B is an 'idler' gear, and its effect is to make the final gear (C) turn in the same direction as the first gear (A).
Question 5: A driver gear with 50 teeth rotates at 100 RPM. It drives a gear with 25 teeth. What is the rotational speed of the smaller gear?
- 50 RPM
- 100 RPM
- 200 RPM (Correct answer)
- 400 RPM
Correct answer: 200 RPM
The speeds are inversely proportional to the number of teeth. The ratio is 50:25 or 2:1. This means the smaller gear will turn twice as fast as the larger gear. Speed of small gear = 100 RPM * (50 / 25) = 100 * 2 = 200 RPM.
Question 6: What is the primary purpose of a rack and pinion gear system?
- To change the direction of rotation
- To convert rotational motion to linear motion (Correct answer)
- To increase torque significantly
- To disengage the drive shaft
Correct answer: To convert rotational motion to linear motion
A rack and pinion system is used to convert rotational motion into linear motion, or vice versa. The pinion is a circular gear that engages with the teeth on the rack, which is a linear gear bar. This mechanism is commonly found in vehicle steering systems.
Question 7: Two gears are meshed. Gear A has 60 teeth and Gear B has 20 teeth. For every one full rotation of Gear A, how many rotations does Gear B complete?
- One-third
- One
- Three (Correct answer)
- Sixty
Correct answer: Three
The gear ratio is 60:20, which simplifies to 3:1. This means that for every one rotation of the larger gear (A), the smaller gear (B) must complete three rotations to make all 60 teeth of gear A pass by.
Free DAA Mechanical Comprehension: Gears and Cogs Questions and Answers
If Gear A turns clockwise and is meshed directly with Gear B, which way will Gear B turn?