OAR OAR Mechanical Reasoning 2 — Questions and Answers
Question 1: A lever is 10 feet long with the fulcrum 2 feet from the load end. If a 400 lb load is placed on the short end, how much force is needed on the long end to balance it?
- 100 lb (Correct answer)
- 150 lb
- 200 lb
- 300 lb
Correct answer: 100 lb
Using the lever principle: 400 × 2 = F × 8, so F = 100 lb.
Question 2: Water flows through a pipe that narrows from 4 inches in diameter to 2 inches. Compared to the wide section, the water speed in the narrow section is:
- Half as fast
- The same speed
- Twice as fast
- Four times as fast (Correct answer)
Correct answer: Four times as fast
Flow rate is constant; halving the diameter quarters the area, so speed quadruples.
Question 3: A block sits on a ramp inclined at 30°. The component of gravity acting parallel to the ramp surface (pulling the block down the slope) equals:
- mg × cos30°
- mg × sin30° (Correct answer)
- mg × tan30°
- mg × sin60°
Correct answer: mg × sin30°
The component of gravity along an incline is mg × sinθ.
Question 4: Two gears mesh together. Gear A has 12 teeth and Gear B has 36 teeth. If Gear A turns at 180 RPM, what is the speed of Gear B?
- 20 RPM
- 30 RPM
- 45 RPM
- 60 RPM (Correct answer)
Correct answer: 60 RPM
Gear ratio = 12/36 = 1/3, so Gear B turns at 180 × (1/3) = 60 RPM.
Question 5: A spring with a spring constant of 50 N/m is compressed 0.4 m from its natural length. How much potential energy is stored in the spring?
- 4 J (Correct answer)
- 10 J
- 20 J
- 40 J
Correct answer: 4 J
Elastic potential energy = ½kx² = ½ × 50 × 0.16 = 4 J.
Question 6: Which type of wrench provides the greatest mechanical advantage when loosening a very tight bolt?
- A short open-end wrench
- A box wrench
- A long breaker bar (Correct answer)
- A socket wrench with a short handle
Correct answer: A long breaker bar
A longer handle increases the torque (force × distance) applied to the bolt.
Question 7: A hydraulic jack has an input piston with area 2 in² and an output piston with area 20 in². If 50 lb of force is applied to the input, what load can the output lift?
- 5 lb
- 50 lb
- 500 lb (Correct answer)
- 5,000 lb
Correct answer: 500 lb
Pressure is equal throughout: F_out = F_in × (A_out/A_in) = 50 × 10 = 500 lb.
OAR OAR Mechanical Reasoning 2
A lever is 10 feet long with the fulcrum 2 feet from the load end.
If a 400 lb load is placed on the short end, how much force is needed on the long end to balance it?