Mechanical Engineering - MCQ Practice Questions

A Carnot refrigerator operates between T_H = 300 K and T_C = 250 K. Its coefficient of performance (COP) is:

The Clausius-Clapeyron equation relates vapor pressure to:

For a system undergoing a reversible process from state 1 to state 2, which statement is true?

In a turbojet engine operating on a Brayton cycle, if the pressure ratio r_p increases, the thermal efficiency:

Maxwell relations are derived from the equality of:

In an Otto cycle engine with compression ratio r = 9 and γ = 1.4, the thermal efficiency is approximately:

In a diesel engine, if the cutoff ratio is 1.5 and compression ratio is 16, calculate the thermal efficiency. (Assume γ = 1.4)

In a gas turbine Brayton cycle, air enters the compressor at 300 K and 100 kPa. The pressure ratio is 8. If γ = 1.4 and R = 287 J/kg·K, find the compressor outlet temperature (assuming isentropic compression).

A Carnot heat pump operates between 270 K and 330 K. If 1000 J of work is supplied, how much heat is delivered to the hot reservoir?

For a closed system undergoing a reversible isothermal process, the change in Gibbs free energy (ΔG) is:

A Rankine cycle (ideal steam cycle) is used in thermal power plants. Which process has the highest irreversibility?

For a real gas undergoing Joule-Thomson expansion through a throttle valve, the Joule-Thomson coefficient (μ_JT) is negative. This means:

In a diesel cycle, the expansion process (power stroke) is adiabatic. If the pressure and temperature at the end of compression are 40 bar and 850 K respectively, and the expansion ratio is 8, what is approximately the temperature at the end of expansion? (Take γ = 1.4)

A compressor compresses air from 1 bar and 25°C to 8 bar. If the isentropic efficiency is 0.80 and the process is adiabatic, what is the actual temperature of air after compression? (γ = 1.4, R = 287 J/kg·K)

An open system (control volume) has mass entering at 50 kg/s with specific enthalpy 200 kJ/kg and mass leaving at 50 kg/s with specific enthalpy 350 kJ/kg. The rate of work done ON the system is 2 MW. Neglecting KE and PE changes, the rate of heat transfer is:

For a polytropic process PVⁿ = constant with n=1.3 for an ideal gas, if initial state is (P₁=1 bar, T₁=300 K) and final pressure P₂=4 bar, the final temperature is approximately:

A reciprocating compressor compresses air from 1 bar, 300 K to 10 bar. If the process follows PVⁿ = constant with n=1.25, what is the specific work required per kg of air? (R=287 J/kg·K)

A Rankine cycle operates between 8 MPa (saturation temp ≈ 295°C) and 0.01 MPa (saturation temp ≈ 45°C). The isentropic efficiency of the turbine is 85%. If inlet enthalpy to turbine is 2800 kJ/kg and exit enthalpy for isentropic expansion is 2300 kJ/kg, the actual exit enthalpy is:

A steam turbine receives steam at 5 MPa, 400°C with an enthalpy of 3231 kJ/kg. It exits at 0.1 MPa with enthalpy 2675 kJ/kg. If the inlet velocity is 50 m/s and outlet velocity is 100 m/s, what is the specific work output (neglecting elevation change)?

A horizontal pipe carries water at steady state. At section 1: P₁ = 200 kPa, V₁ = 3 m/s. At section 2: V₂ = 6 m/s. Assuming ideal incompressible flow and neglecting friction, the pressure at section 2 is: