WTMA Wheels, Axles, and Rotation 4 — Questions and Answers
Question 1: A flywheel stores energy by spinning at high speed. Which property MOST determines how much energy it can store?
- Its color
- Its rotational speed and mass distribution (Correct answer)
- The material of its axle
- The number of spokes
Correct answer: Its rotational speed and mass distribution
Rotational kinetic energy depends on both the moment of inertia (how mass is distributed) and the square of rotational speed.
Question 2: Gear A (driver, 12 teeth) meshes directly with Gear B (36 teeth). Gear A rotates at 900 RPM. What is Gear B's speed?
- 300 RPM (Correct answer)
- 900 RPM
- 2700 RPM
- 450 RPM
Correct answer: 300 RPM
Speed of Gear B = (teeth of A / teeth of B) × speed of A = (12/36) × 900 = 300 RPM.
Question 3: A hand truck (dolly) has small wheels. Replacing them with larger-diameter wheels would primarily:
- Make it harder to push over obstacles
- Reduce the load capacity
- Make it easier to roll over obstacles and reduce rolling resistance (Correct answer)
- Increase the mechanical advantage of the handles
Correct answer: Make it easier to roll over obstacles and reduce rolling resistance
Larger wheels have a higher ratio of radius to obstacle height, allowing them to roll over bumps more easily, and larger wheels generally have lower rolling resistance.
Question 4: In a clock, the minute hand completes one revolution per hour. The hour hand completes one revolution every 12 hours. What is the gear ratio between the mechanisms driving each hand?
- 1:1
- 6:1
- 12:1 (Correct answer)
- 60:1
Correct answer: 12:1
The minute hand turns 12 times for every 1 turn of the hour hand, so the gear ratio is 12:1.
Question 5: A wheel spins at constant speed. A point on the outer rim of the wheel compared to a point halfway to the center has:
- The same linear speed
- Half the linear speed
- Twice the linear speed (Correct answer)
- Four times the linear speed
Correct answer: Twice the linear speed
Linear (tangential) speed = angular speed × radius; at twice the radius, the rim point travels twice the linear speed.
Question 6: Which of the following is an example of a wheel-and-axle simple machine?
- A ramp
- A screwdriver turning a screw (Correct answer)
- A lever
- A pulley block
Correct answer: A screwdriver turning a screw
A screwdriver handle acts as the wheel (large radius) and the shaft acts as the axle (small radius), giving mechanical advantage for turning screws.
Question 7: A drive shaft transfers power from an engine to the rear wheels of a truck. If the drive shaft develops a crack near the center, the MOST likely result is:
- The truck steers more easily
- Vibration, noise, and eventual loss of power to the rear wheels (Correct answer)
- The engine runs faster
- Fuel efficiency improves
Correct answer: Vibration, noise, and eventual loss of power to the rear wheels
A cracked drive shaft causes imbalance leading to vibration and noise, and may fail completely, cutting power transmission to the driven wheels.
WTMA Wheels, Axles, and Rotation 4
A flywheel stores energy by spinning at high speed.
Which property MOST determines how much energy it can store?