WTMA Levers, Pulleys, and Gears 5 โ Questions and Answers
Question 1: A worm gear provides high mechanical advantage. What is a key tradeoff compared to spur gears?
- It runs louder
- It is less efficient due to higher friction (Correct answer)
- It cannot carry heavy loads
- It only works at high speeds
Correct answer: It is less efficient due to higher friction
Worm gears have high friction between the worm and wheel, making them less efficient than spur gears but excellent for high reduction ratios.
Question 2: A force of 40 lb is applied at the handle of a nutcracker 6 inches from the hinge. The nut is 1.5 inches from the hinge. What force is applied to the nut?
- 10 lb
- 40 lb
- 160 lb (Correct answer)
- 240 lb
Correct answer: 160 lb
MA = 6/1.5 = 4; Force on nut = 40 ร 4 = 160 lb.
Question 3: In a pulley system, why is the actual mechanical advantage always less than the ideal mechanical advantage?
- Pulleys spin too fast
- Friction in the pulleys wastes some of the input force (Correct answer)
- The rope stretches and loses energy
- Gravity acts on the pulleys themselves
Correct answer: Friction in the pulleys wastes some of the input force
Friction in the pulley bearings and between the rope and pulley reduces the effective force transmitted.
Question 4: A planetary gear system is commonly used because it:
- Requires no lubrication
- Offers high torque in a compact size (Correct answer)
- Only works in one direction
- Has no moving parts
Correct answer: Offers high torque in a compact size
Planetary gears distribute load across multiple planet gears, providing high torque capacity in a compact, coaxial arrangement.
Question 5: A crow bar is being used to pry open a crate. The crow bar is a:
- Second-class lever
- First-class lever (Correct answer)
- Third-class lever
- Pulley
Correct answer: First-class lever
A crowbar used for prying is a first-class lever โ the fulcrum (edge of crate) is between the effort (your hands) and the load (lid).
Question 6: If the pitch diameter of a drive pulley doubles while the belt speed stays the same, the RPM of that drive pulley:
- Doubles
- Stays the same
- Halves (Correct answer)
- Quadruples
Correct answer: Halves
Belt speed = ฯ ร diameter ร RPM; doubling the diameter at constant belt speed cuts RPM in half.
Question 7: A gear train is designed to reduce speed from 1800 RPM to 300 RPM. What is the overall gear reduction ratio?
- 1:6
- 6:1 (Correct answer)
- 1:3
- 3:1
Correct answer: 6:1
Reduction ratio = input speed รท output speed = 1800 รท 300 = 6, expressed as 6:1.
WTMA Levers, Pulleys, and Gears 5
A worm gear provides high mechanical advantage.
What is a key tradeoff compared to spur gears?