NTN Mechanical Comprehension 3

Question 1

A spring-loaded rescue tool requires 80 pounds of force to compress the spring 4 inches. What is the spring constant (k)?

Accepted Answer

20 lb/in

Answer

Using Hooke's Law: F = kx, where k = F/x = 80 pounds / 4 inches = 20 lb/in.

Question 2

A wheel and axle mechanism has a wheel diameter of 24 inches and an axle diameter of 4 inches. What is the mechanical advantage?

Accepted Answer

6:1

Answer

The mechanical advantage of a wheel and axle = wheel diameter / axle diameter = 24 / 4 = 6:1 (or equivalently, wheel radius / axle radius = 12/2 = 6:1).

Question 3

A fire truck's water tank holds 500 gallons. If water weighs approximately 8.34 pounds per gallon, what is the approximate weight of the water when the tank is full?

Accepted Answer

4,170 pounds

Answer

Weight = volume × density = 500 gallons × 8.34 lb/gal = 4,170 pounds.

Question 4

Two workers push a stalled vehicle. Worker A pushes with 150 pounds of force due east, and Worker B pushes with 200 pounds of force due north. What is the approximate magnitude of the resultant force?

Accepted Answer

250 pounds

Answer

When forces are perpendicular, the resultant is found using the Pythagorean theorem: √(150² + 200²) = √(22,500 + 40,000) = √62,500 = 250 pounds.

Question 5

A belt-driven fan system has a motor pulley with a 6-inch diameter driving a fan pulley with an 18-inch diameter. If the motor runs at 1,800 RPM, what is the fan speed?

Accepted Answer

600 RPM

Answer

In belt-drive systems, the speed ratio is inversely proportional to pulley diameter: Fan RPM = Motor RPM × (Motor diameter / Fan diameter) = 1,800 × (6/18) = 600 RPM.

NTN - National Testing Network Practice Test

NTN - National Testing Network Practice Test

NTN Mechanical Comprehension 3