Test Applying Mechanical Reasoning Questions and Answers Flashcards

A fixed pulley is used to lift a 150 lb load. How much force must be applied to the rope?

Answer: 150 lbs

A fixed pulley only changes the direction of force, not its magnitude; you must still pull with 150 lbs.

Three resistors of 6 ohms each are connected in parallel. What is the total resistance of the circuit?

Answer: 2 ohms

For equal resistors in parallel, total resistance = single resistance ÷ number of resistors = 6 ÷ 3 = 2 ohms.

A gear train consists of three gears in series with 10, 20, and 40 teeth respectively. The first gear drives the second, and the second drives the third. If the first gear turns at 400 RPM, at what speed does the third gear turn?

Answer: 100 RPM

First to second: 400 × (10/20) = 200 RPM; second to third: 200 × (20/40) = 100 RPM.

A 10 lb object rests on a frictionless inclined plane at 30°. What is the component of gravity pulling the object down the slope?

Answer: 5 lbs

The force along the slope = weight × sin(30°) = 10 × 0.5 = 5 lbs.

Which of the following best describes the mechanical advantage of a wedge used to split wood?

Answer: MA = length ÷ width

The mechanical advantage of a wedge equals its length divided by its width — a longer, thinner wedge splits more easily.

Two pistons are connected in a sealed hydraulic system. Piston 1 has an area of 5 sq in and Piston 2 has an area of 25 sq in. If Piston 1 moves down 10 inches, how far does Piston 2 move up?

Answer: 2 inches

Volume displaced is constant; Piston 1 volume = 5 × 10 = 50 cu in; Piston 2 moves 50 ÷ 25 = 2 inches.

A mechanic applies 80 lbs of force at the end of a 15-inch breaker bar to loosen a bolt. What is the torque applied to the bolt?

Answer: 1200 lb-in

Torque = force × moment arm = 80 lbs × 15 inches = 1200 lb-in.