OAR OAR Mechanical Comprehension: Simple Machines 5 — Questions and Answers
Question 1: A lever balances when the torque on each side is equal. If a 60 N load sits 2 m from the fulcrum, what effort is needed 4 m from the fulcrum?
- 120 N
- 60 N
- 30 N (Correct answer)
- 15 N
Correct answer: 30 N
Torque balance: effort × 4 = 60 × 2, so effort = 120/4 = 30 N.
Question 2: Which of the following is NOT a simple machine?
- Lever
- Pulley
- Spring (Correct answer)
- Wedge
Correct answer: Spring
The six simple machines are lever, wheel and axle, pulley, inclined plane, wedge, and screw — a spring is not one of them.
Question 3: A block and tackle system with 3 movable pulleys and 3 fixed pulleys has approximately what mechanical advantage?
- 3
- 6 (Correct answer)
- 9
- 12
Correct answer: 6
A block and tackle with 3 movable pulleys provides a mechanical advantage of 6 (twice the number of movable pulleys).
Question 4: When you tighten a jar lid using your fingers, the lid acts as which component of a wheel and axle?
- The wheel
- The axle (Correct answer)
- The fulcrum
- The effort arm
Correct answer: The axle
The jar lid is the axle (smaller radius); your hand gripping the outside acts as the wheel (larger radius) applying torque.
Question 5: An inclined plane has a mechanical advantage of 5. If the load weighs 300 N, how much effort force is required (ignoring friction)?
- 30 N
- 60 N (Correct answer)
- 150 N
- 1500 N
Correct answer: 60 N
Effort = load / MA = 300 / 5 = 60 N.
Question 6: Which of the following best describes the trade-off when using any simple machine?
- You gain both force and speed simultaneously
- You gain force but must apply it over a greater distance (Correct answer)
- You gain distance but must apply greater force
- You gain energy from the machine itself
Correct answer: You gain force but must apply it over a greater distance
Simple machines conserve energy; gaining mechanical advantage (more force) always requires moving through a greater distance.
Question 7: A doorknob is an example of which simple machine?
- Lever
- Screw
- Wheel and axle (Correct answer)
- Wedge
Correct answer: Wheel and axle
A doorknob is a wheel and axle — the knob is the wheel (large radius) and the spindle is the axle (small radius).
OAR OAR Mechanical Comprehension: Simple Machines 5
A lever balances when the torque on each side is equal.
If a 60 N load sits 2 m from the fulcrum, what effort is needed 4 m from the fulcrum?