Free DAA Mechanical Comprehension: Gears and Cogs Questions and Answers

Question 1

If Gear A turns clockwise and is meshed directly with Gear B, which way will Gear B turn?

Accepted Answer

Counter-clockwise

Answer

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?

Accepted Answer

4:1

Answer

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?

Accepted Answer

Speed decreases, torque increases

Answer

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?

Accepted Answer

Clockwise

Answer

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?

Accepted Answer

200 RPM

Answer

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.

DAA - Defence Aptitude Assessment Practice Test

DAA - Defence Aptitude Assessment Practice Test

Free DAA Mechanical Comprehension: Gears and Cogs Questions and Answers