NTN Mechanical Comprehension 2

Question 1

A firefighter needs to pry open a door using a halligan bar. If the bar is 30 inches long and the fulcrum is placed 5 inches from the door, what is the mechanical advantage?

Accepted Answer

5:1

Answer

Mechanical advantage of a lever = effort arm / load arm = 25 inches / 5 inches = 5:1. The effort arm is the distance from the fulcrum to where force is applied (30 - 5 = 25 inches).

Question 2

Two gears are meshed together. Gear A has 40 teeth and Gear B has 20 teeth. If Gear A rotates at 100 RPM, how fast does Gear B rotate?

Accepted Answer

200 RPM

Answer

When gears mesh, the gear ratio is inversely proportional to teeth count. Gear B speed = (Gear A teeth / Gear B teeth) × Gear A speed = (40/20) × 100 = 200 RPM.

Question 3

A pump system uses a pipe with a 4-inch diameter that narrows to a 2-inch diameter. According to the continuity equation, how does the water velocity change at the narrower section?

Accepted Answer

Velocity quadruples

Answer

By the continuity equation (A₁V₁ = A₂V₂), when the diameter halves, the cross-sectional area becomes one-quarter (area ∝ diameter²), so velocity must quadruple to maintain the same flow rate.

Question 4

A rope and pulley system uses three supporting ropes to lift a rescue basket. If the basket and patient weigh 300 pounds, approximately how much force must the rescuer apply (ignoring friction)?

Accepted Answer

100 pounds

Answer

In an ideal pulley system with 3 supporting ropes, the force required equals the load divided by the number of supporting ropes: 300 / 3 = 100 pounds.

Question 5

A hydraulic jack has a small piston with an area of 2 square inches and a large piston with an area of 20 square inches. If 50 pounds of force is applied to the small piston, what force is generated at the large piston?

Accepted Answer

500 pounds

Answer

Pascal's principle states that pressure is transmitted equally. Force₂ = Force₁ × (Area₂ / Area₁) = 50 × (20/2) = 500 pounds.

NTN - National Testing Network Practice Test

NTN - National Testing Network Practice Test

NTN Mechanical Comprehension 2