TalentLens Mechanical Comprehension 2 — Questions and Answers
Question 1: A wheel with a radius of 2 ft is attached to a wheel with a radius of 4 ft. If the smaller wheel rotates at 60 RPM, how fast does the larger wheel rotate?
- 15 RPM
- 30 RPM (Correct answer)
- 120 RPM
- 240 RPM
Correct answer: 30 RPM
Gear/wheel ratio: smaller turns at 60 RPM, larger is twice the radius, so it turns at 60 ÷ 2 = 30 RPM.
Question 2: A hydraulic jack has an input piston of 2 sq in and an output piston of 20 sq in. If you apply 50 lbs of force to the input, what output force is produced?
- 50 lbs
- 100 lbs
- 500 lbs (Correct answer)
- 1000 lbs
Correct answer: 500 lbs
Pascal's law: output force = (output area / input area) × input force = (20/2) × 50 = 500 lbs.
Question 3: Which type of beam deflects the least when a load is applied at its center?
- A longer beam of the same material
- A shorter beam of the same material (Correct answer)
- A beam with smaller cross-section
- A beam made of a more flexible material
Correct answer: A shorter beam of the same material
Shorter beams deflect less because deflection increases with the cube of the span length.
Question 4: A ball rolls down a frictionless ramp and onto a flat surface. What happens to its speed on the flat surface?
- It continues to accelerate
- It remains constant (Correct answer)
- It gradually slows down
- It immediately stops
Correct answer: It remains constant
With no friction and no slope, there is no net force, so by Newton's first law the speed stays constant.
Question 5: A solid cylinder and a hollow cylinder of the same mass and outer radius roll down a ramp. Which reaches the bottom first?
- The hollow cylinder
- The solid cylinder (Correct answer)
- They arrive at the same time
- It depends on the ramp angle
Correct answer: The solid cylinder
The solid cylinder has a lower moment of inertia, so less energy goes into rotation and more into translation, making it faster.
Question 6: Two blocks connected by a rope over a frictionless pulley sit on a frictionless table. One block is pushed toward the pulley. What happens to the tension in the rope?
- Tension increases
- Tension decreases
- Tension stays the same
- Tension becomes zero (Correct answer)
Correct answer: Tension becomes zero
If the block is pushed toward the pulley (slack rope), the rope goes slack and tension drops to zero.
Question 7: A wrench 12 inches long applies a torque of 60 ft-lbs. Approximately how much force is applied?
- 5 lbs
- 60 lbs (Correct answer)
- 720 lbs
- 72 lbs
Correct answer: 60 lbs
Torque = Force × distance; 12 in = 1 ft, so Force = 60 ft-lbs ÷ 1 ft = 60 lbs.
TalentLens Mechanical Comprehension 2
A wheel with a radius of 2 ft is attached to a wheel with a radius of 4 ft.
If the smaller wheel rotates at 60 RPM, how fast does the larger wheel rotate?