TalentLens Mechanical Comprehension 2

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?

Accepted Answer

30 RPM

Answer

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?

Accepted Answer

500 lbs

Answer

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?

Accepted Answer

A shorter beam of the same material

Answer

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?

Accepted Answer

It remains constant

Answer

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?

Accepted Answer

The solid cylinder

Answer

The solid cylinder has a lower moment of inertia, so less energy goes into rotation and more into translation, making it faster.

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TalentLens Mechanical Comprehension 2