Ultimate Questions and Answers Flashcards
6 cards from real MECHANICAL APTITUDE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Ultimate Questions and Answers flashcards as text
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?
Answer: 30 cm
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.
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?
Answer: 133.3N
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.
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?
Answer: 5 MPa
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.
An electric motor draws 10 amps at 240 volts and produces 2 kW of mechanical output. What is the motor's efficiency?
Answer: 83.3%
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.
What is the factor of safety if a component's ultimate tensile strength is 450 MPa and the maximum working stress is 150 MPa?
Answer: 3.0
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.
A heat engine operates between temperatures of 600K (hot reservoir) and 300K (cold reservoir). What is its maximum possible (Carnot) efficiency?
Answer: 50%
Carnot efficiency = 1 - (T_cold/T_hot) = 1 - (300/600) = 1 - 0.5 = 0.5 = 50%. No real engine can exceed this theoretical maximum when operating between these temperatures.