WTMA Mechanical Comprehension 3 — Questions and Answers
Question 1: A spring is compressed 3 inches by a 30-lb force. Following Hooke's Law, how much force is needed to compress it 5 inches?
- 18 lbs
- 30 lbs
- 50 lbs (Correct answer)
- 150 lbs
Correct answer: 50 lbs
Hooke's Law: force is proportional to displacement. The spring constant = 30/3 = 10 lb/in, so 5 in × 10 lb/in = 50 lbs.
Question 2: Which of the following is an example of a third-class lever?
- A wheelbarrow
- A seesaw
- A fishing rod (Correct answer)
- A bottle opener
Correct answer: A fishing rod
In a third-class lever the effort is between the fulcrum and the load, as in a fishing rod where the hand applies effort between the pivot point and the fish.
Question 3: Air pressure in a tire is measured in PSI. If the tire's internal volume decreases by half (without leaking), what happens to the pressure?
- It stays the same
- It doubles (Correct answer)
- It is cut in half
- It drops to zero
Correct answer: It doubles
Boyle's Law states that pressure and volume are inversely proportional at constant temperature, so halving the volume doubles the pressure.
Question 4: A block-and-tackle system uses two movable pulleys. What is its mechanical advantage?
- 1
- 2
- 3
- 4 (Correct answer)
Correct answer: 4
Each movable pulley doubles the mechanical advantage, so two movable pulleys provide a mechanical advantage of 4.
Question 5: Two pipes carry water to a tank. Pipe A has a diameter of 2 inches and Pipe B has a diameter of 4 inches. At equal water pressure, which pipe delivers more water?
- Pipe A, because smaller pipes have higher pressure
- Pipe B, because a larger cross-section allows greater flow (Correct answer)
- Both deliver the same amount
- It depends on the pipe material
Correct answer: Pipe B, because a larger cross-section allows greater flow
Flow rate depends on cross-sectional area; Pipe B's area (πr²) is four times that of Pipe A, so it carries four times more water.
Question 6: A nail is an example of which simple machine?
- Lever
- Pulley
- Wedge (Correct answer)
- Wheel and axle
Correct answer: Wedge
A nail's pointed tip is a wedge, converting the downward force of a hammer into an outward splitting force that drives the nail into wood.
Question 7: When you tighten a bolt with a wrench that has a 12-inch handle versus an 8-inch handle (applying the same force), how does the torque compare?
- The 12-inch wrench produces less torque
- The 12-inch wrench produces equal torque
- The 12-inch wrench produces 50% more torque (Correct answer)
- The 12-inch wrench produces twice the torque
Correct answer: The 12-inch wrench produces 50% more torque
Torque = force × lever arm length; 12/8 = 1.5, so the longer wrench produces 50% more torque with the same applied force.
WTMA Mechanical Comprehension 3
A spring is compressed 3 inches by a 30-lb force.
Following Hooke's Law, how much force is needed to compress it 5 inches?