Mechanical Aptitude Ultimate Questions and Answers 3

Question 1

A belt drive system has a driving pulley of 10 cm diameter spinning at 1,800 RPM. If the driven pulley must spin at 600 RPM, what diameter should it be?

Accepted Answer

30 cm

Answer

For belt drives: D₁ × N₁ = D₂ × N₂. Therefore D₂ = D₁ × N₁ / N₂ = 10 × 1800/600 = 30 cm. The driven pulley must be 3 times larger to turn at 1/3 the speed.

Question 2

A lever arm is 2 meters long with the fulcrum 0.5 meters from the load. If the load is 400N, what effort force is needed to balance it?

Accepted Answer

133.3N

Answer

The effort arm is 2 - 0.5 = 1.5 meters. By the principle of moments: Effort × 1.5 = 400 × 0.5. Effort = 200/1.5 = 133.3N.

Question 3

A pipe with internal pressure of 500 kPa has an inner diameter of 200 mm and a wall thickness of 10 mm. What is the hoop stress in the pipe wall?

Accepted Answer

5 MPa

Answer

Hoop stress (σ) for a thin-walled pressure vessel is σ = Pr/t, where P is pressure, r is inner radius, and t is wall thickness. σ = 500,000 × 0.1 / 0.01 = 5,000,000 Pa = 5 MPa.

Question 4

An electric motor draws 10 amps at 240 volts and produces 2 kW of mechanical output. What is the motor's efficiency?

Accepted Answer

83.3%

Answer

Electrical input power = V × I = 240 × 10 = 2,400 W. Efficiency = output/input × 100% = 2,000/2,400 × 100% = 83.3%. The remaining 400W is lost as heat in the motor windings and friction.

Question 5

What is the factor of safety if a component's ultimate tensile strength is 450 MPa and the maximum working stress is 150 MPa?

Accepted Answer

3.0

Answer

Factor of Safety (FoS) = Ultimate Strength / Working Stress = 450 MPa / 150 MPa = 3.0. This means the component can withstand 3 times the maximum expected load before failure.

Mechanical Aptitude Test Practice Test

Mechanical Aptitude Test Practice Test

Mechanical Aptitude Ultimate Questions and Answers 3