Bennett Mechanical Gears and Belt Drives Questions and Answers 1 — Questions and Answers
Question 1: In the gear train shown, the driver gear A has 40 teeth and rotates clockwise. Gear B has 20 teeth, and Gear C has 40 teeth. In which direction and at what relative speed does Gear C rotate compared to Gear A?
- Clockwise, at the same speed as Gear A. (Correct answer)
- Counter-clockwise, faster than Gear A.
- Clockwise, slower than Gear A.
- Counter-clockwise, at the same speed as Gear A.
Correct answer: Clockwise, at the same speed as Gear A.
Gear A turns clockwise, causing the intermediate gear (B) to turn counter-clockwise. Gear B then causes Gear C to turn clockwise. Since Gear A and Gear C have the same number of teeth (40), they will rotate at the same speed. The idler gear (B) only serves to change the direction of rotation.
Question 2: A small pulley (X) is connected to a large pulley (Y) by a crossed belt. If pulley X rotates counter-clockwise, what will be the motion of pulley Y?
- It will rotate counter-clockwise and slower.
- It will rotate clockwise and faster.
- It will not rotate.
- It will rotate clockwise and slower. (Correct answer)
Correct answer: It will rotate clockwise and slower.
A crossed belt causes the driven pulley to rotate in the opposite direction of the driver pulley. Since pulley X is rotating counter-clockwise, pulley Y will rotate clockwise. Because pulley Y is larger than pulley X, it will complete fewer revolutions in the same amount of time, meaning it rotates slower.
Question 3: If gear X makes 10 full rotations, how many full rotations will gear Z make?
- 5
- 10
- 20 (Correct answer)
- 40
Correct answer: 20
Gear X has twice as many teeth as Gear Y, so for every one rotation of X, Y rotates twice (Gear Ratio 1:2). Gear Y and Gear Z are the same size. Therefore, for every 10 rotations of X, Y will rotate 20 times, and Z will also rotate 20 times. The final speed is determined by the ratio of the first and last gears in this simple train.
Question 4: Which of the following arrangements would result in the greatest increase in torque from the driver shaft to the driven shaft?
- A large driver gear turning a small driven gear.
- A small driver gear turning a large driven gear. (Correct answer)
- Two gears of the same size connected by a chain.
- Two pulleys of the same size connected by a belt.
Correct answer: A small driver gear turning a large driven gear.
Torque and speed have an inverse relationship in a gear system. To increase torque, you must decrease speed. This is achieved when a small driver gear (high speed, low torque) turns a large driven gear (low speed, high torque).
Question 5: Two pulleys are connected by a standard, un-crossed belt. The driver pulley has a diameter of 10 inches and the driven pulley has a diameter of 5 inches. If the driver pulley rotates at 100 RPM, what is the speed of the driven pulley?
- 50 RPM
- 100 RPM
- 200 RPM (Correct answer)
- 25 RPM
Correct answer: 200 RPM
The speeds of pulleys in a belt drive are inversely proportional to their diameters. The driven pulley is half the diameter of the driver pulley (10 inches / 5 inches = 2). Therefore, the driven pulley will rotate twice as fast as the driver pulley (100 RPM * 2 = 200 RPM).
Question 6: If the handle is turned clockwise as indicated by the arrow, which direction will the rack (toothed bar) move?
- Up
- To the left
- Down
- To the right (Correct answer)
Correct answer: To the right
Turning the handle clockwise turns the top gear clockwise. This gear is meshed with the lower gear, causing the lower gear to rotate counter-clockwise. The teeth on the bottom of the counter-clockwise rotating gear engage the rack and will push it to the right.
Bennett Mechanical Gears and Belt Drives Questions and Answers 1
In the gear train shown, the driver gear A has 40 teeth and rotates clockwise.
Gear B has 20 teeth, and Gear C has 40 teeth.
In which direction and at what relative speed does Gear C rotate compared to Gear A?