FCTC FCTC Mechanical Reasoning Principles Questions and Answers 3

Question 1

A hydraulic jack uses a small piston with an area of 2 sq in and a large piston with an area of 20 sq in. If 50 lbs of force is applied to the small piston, what force does the large piston exert?

Accepted Answer

500 lbs

Answer

Pascal's Law states that pressure is equal throughout a closed hydraulic system; 50 lbs ÷ 2 sq in = 25 psi, and 25 psi × 20 sq in = 500 lbs.

Question 2

A bolt has 20 threads per inch. How many full turns are required to advance the bolt 1.5 inches?

Accepted Answer

30 turns

Answer

Multiplying the number of threads per inch (20) by the desired advancement (1.5 in) gives 30 full turns.

Question 3

Two meshing gears have 12 teeth and 36 teeth respectively. If the smaller gear rotates at 180 RPM, what is the speed of the larger gear?

Accepted Answer

60 RPM

Answer

Gear ratio is 12:36 = 1:3, so the larger gear turns at 180 ÷ 3 = 60 RPM.

Question 4

A spring stretches 4 inches when a 20 lb load is applied. How far will it stretch under a 35 lb load (assuming it remains within its elastic limit)?

Accepted Answer

7 in

Answer

Hooke's Law gives a spring constant of 20 ÷ 4 = 5 lb/in; 35 ÷ 5 = 7 inches.

Question 5

A class 2 lever has the fulcrum at one end, the load 3 ft from the fulcrum, and the effort applied 9 ft from the fulcrum. What is the mechanical advantage?

Accepted Answer

3

Answer

Mechanical advantage = effort arm ÷ load arm = 9 ft ÷ 3 ft = 3.

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FCTC FCTC Mechanical Reasoning Principles Questions and Answers 3