# Class Test - Elements Of Mechanical Engineering (Meci 101)

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Shailendra Kumar
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Quizzes Created: 1 | Total Attempts: 145
Questions: 20 | Attempts: 145

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• 1.

### For a process from state 1 to state 2, heat transfer in a reversible process is given by

• A.

Q for reversible=(To)*(S1-S2)

• B.

Q for reversible=(To)*(S2-S1)

• C.

Q for reversible=(To)/(S1-S2)

• D.

Q for reversible=(To)/(S2-S1)

B. Q for reversible=(To)*(S2-S1)
Explanation
The correct answer is Q for reversible=(To)*(S2-S1). This equation represents the heat transfer in a reversible process from state 1 to state 2. The temperature difference (To) is multiplied by the entropy change (S2-S1) to calculate the heat transfer. This equation follows the general formula for heat transfer in a reversible process, where the heat transfer is proportional to the temperature difference and the entropy change.

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• 2.

### Which of the following is true?

• A.

Q for reversible > Q for irreversible and work for reversible < work for irreversible

• B.

Q for reversible < Q for irreversible and work for reversible > work for irreversible

• C.

Q for reversible < Q for irreversible and work for reversible < work for irreversible

• D.

Q for reversible > Q for irreversible and work for reversible > work for irreversible

D. Q for reversible > Q for irreversible and work for reversible > work for irreversible
• 3.

### Which of the following is true for a steady flow system?

• A.

Mass entering = mass leaving

• B.

Mass does not enter or leave the system

• C.

Mass entering can be more or less than the mass leaving

• D.

None of the mentioned

A. Mass entering = mass leaving
Explanation
In a steady flow system, the mass entering the system is equal to the mass leaving the system. This means that there is no net change in mass within the system over time. This is a fundamental principle in the study of fluid mechanics and is applicable to various engineering systems, such as pipelines or heat exchangers.

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• 4.

### The work done by a closed system in a reversible process is always ___ that done in an irreversible process.

• A.

Less than or more than

• B.

Equal to

• C.

Less than

• D.

More than

D. More than
Explanation
In a reversible process, the work done by a closed system is always greater than that done in an irreversible process. This is because in a reversible process, the system can adjust its internal conditions to match the external conditions, resulting in a more efficient transfer of energy. In contrast, an irreversible process does not allow for this adjustment and therefore leads to less work done by the system.

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• 5.

### A piston-cylinder contains air at 600 kPa, 290 K and a volume of 0.01m^3. A constant pressure process gives 54 kJ of work out. Find the final volume of the air.

• A.

0.05 m^3

• B.

0.01 m^3

• C.

0.10 m^3

• D.

0.15 m^3

C. 0.10 m^3
Explanation
In a constant pressure process, the work done is given by the formula W = P * (Vf - Vi), where W is the work done, P is the pressure, Vf is the final volume, and Vi is the initial volume. We are given the initial pressure, volume, and the work done. We need to find the final volume. Rearranging the formula, we get Vf = Vi + (W / P). Substituting the given values, we get Vf = 0.01 m^3 + (54 kJ / 600 kPa). Simplifying, we find Vf = 0.01 m^3 + 0.09 m^3 = 0.10 m^3. Therefore, the final volume of the air is 0.10 m^3.

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• 6.

### A piston-cylinder contains 0.5 kg of air at 500 kPa and 500 K. The air expands in a process so the pressure is linearly decreasing with volume to a final state of 100 kPa and 300 K. Find the work in the process.

• A.

56.1 kJ

• B.

66.1 kJ

• C.

76.1 kJ

• D.

86.1 kJ

D. 86.1 kJ
Explanation
In this problem, the work done by the air can be calculated using the equation for work in a piston-cylinder system, which is given by W = P(V2 - V1), where W is the work done, P is the pressure, V2 is the final volume, and V1 is the initial volume. Given that the pressure decreases linearly with volume, we can assume that the process is quasi-static and use the average pressure, which is (P1 + P2)/2, where P1 is the initial pressure and P2 is the final pressure. The initial and final volumes can be determined using the ideal gas law, PV = mRT, where P is the pressure, V is the volume, m is the mass, R is the gas constant, and T is the temperature. Using these equations and the given values, we can calculate the work to be 86.1 kJ.

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• 7.

### When a body A is in thermal equilibrium with a body B, and also separately with a body C, then B and C will be in thermal equilibrium with each other.

• A.

True

• B.

False

A. True
Explanation
When two bodies, A and B, are in thermal equilibrium with each other, it means that there is no net transfer of heat between them. Similarly, when body A is separately in thermal equilibrium with body C, it also implies that there is no net transfer of heat between them. Therefore, if body A is in thermal equilibrium with both body B and body C, it follows that there is no net transfer of heat between B and C as well. Hence, B and C will be in thermal equilibrium with each other.

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• 8.

### What is the standard fixed point of thermometry?

• A.

The ice point

• B.

The steam point

• C.

The triple point of water

• D.

None of the mentioned

C. The triple point of water
Explanation
The standard fixed point of thermometry is the triple point of water. This is because at the triple point, water exists in a stable equilibrium between its solid, liquid, and gaseous phases. The temperature and pressure at the triple point are well-defined and can be used as reference points for calibrating temperature measuring devices. The ice point and steam point are also commonly used as fixed points, but the triple point of water is considered the most accurate and precise standard fixed point for thermometry.

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• 9.

### Which of the following is chosen as the standard thermometric substance?

• A.

Gas

• B.

Liquid

• C.

Solid

• D.

All of the mentioned

A. Gas
Explanation
Gas is chosen as the standard thermometric substance because it has the advantage of expanding uniformly with temperature changes, making it easier to measure accurately. Gas thermometers rely on the relationship between temperature and pressure, such as the ideal gas law, to determine temperature. This allows for precise and consistent measurements, making gas the preferred choice for standardizing temperature scales. Liquids and solids may not exhibit the same level of uniform expansion and can be more difficult to measure accurately.

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• 10.

### Work done by a system is taken to be

• A.

Positive

• B.

Negative

• C.

Zero

• D.

Varies according to situation

A. Positive
Explanation
Work done by a system is taken to be positive because work is considered to be done on the system when there is a transfer of energy into the system. This means that the system is gaining energy, which is represented by a positive value. Conversely, when work is done by the system, there is a transfer of energy out of the system, resulting in a decrease in the system's energy. In this case, work is considered negative. Therefore, the work done by a system is generally taken to be positive unless specified otherwise.

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• 11.

### Work is a

• A.

Point function

• B.

Path function

• C.

Depends on the state

• D.

None of the mentioned

A. Point function
Explanation
A point function is a type of function in thermodynamics that depends only on the initial and final states of a system, and not on the path taken between those states. Work is a point function because the amount of work done on or by a system is determined solely by the initial and final states of the system, regardless of the specific path taken to reach those states. This means that the work done is independent of the process or the steps involved in achieving the change in state.

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• 12.

### The differentials of point functions are

• A.

Perfect differentials

• B.

Exact differentials

• C.

All of the mentioned

• D.

none of the mentioned

C. All of the mentioned
Explanation
The correct answer is "all of the mentioned". In calculus, a perfect differential is a differential form that can be expressed as the total differential of a function. An exact differential is a differential form that can be integrated to obtain a function. Both perfect differentials and exact differentials are types of point functions, which means they depend only on the current state of a system and not on the path taken to reach that state. Therefore, all of the mentioned options are correct.

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• 13.

### Constant pressure process is also known as

• A.

Isopiestic process

• B.

Isobaric process

• C.

All of the mentioned

• D.

None of the mentioned

B. Isobaric process
Explanation
The correct answer is "isobaric process." In a constant pressure process, the pressure remains constant throughout the system. This means that the system is undergoing a process where the pressure is not changing. Isobaric specifically refers to a process where the pressure remains constant, so it is the correct term to describe a constant pressure process. Therefore, the answer "isobaric process" is the most suitable option.

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• 14.

### Work done in a quasi-static process

• A.

Depends on the path followed

• B.

Independent of the path followed

• C.

Depends only on the initial and final states

• D.

None of the mentioned

A. Depends on the path followed
Explanation
In a quasi-static process, the work done depends on the path followed. This means that the amount of work done can vary depending on the specific steps taken to go from the initial state to the final state. The path followed can involve different intermediate states and different amounts of work done at each step. Therefore, the work done is not independent of the path and cannot be solely determined by the initial and final states.

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• 15.

### Shaft uses which kind of motion to do work?

• A.

Vertical motion

• B.

Horizontal motion

• C.

Rotational motion

• D.

None of the mentioned

C. Rotational motion
Explanation
A shaft uses rotational motion to do work. A shaft is a long, cylindrical mechanical component that is used to transmit power and motion between different parts of a machine. It rotates on its axis, allowing it to transfer rotational energy and perform various tasks such as driving gears, wheels, or other components. Vertical and horizontal motions are not typically associated with the function of a shaft, making them incorrect options.

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• 16.

### Thermodynamic properties are

• A.

Point function

• B.

Path function

• C.

Depends on the state

• D.

None of the mentioned

A. Point function
Explanation
Thermodynamic properties are classified as point functions because they only depend on the current state of the system and not on the path taken to reach that state. Point functions are independent of the process or history of the system and can be determined solely by the initial and final states. This means that the value of a thermodynamic property, such as temperature or pressure, does not change if the system is taken through different paths to reach the same final state.

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• 17.

### Cyclic integral of a property is always

• A.

Zero

• B.

One

• C.

Infinite value

• D.

None of the mentioned

A. Zero
Explanation
The cyclic integral of a property refers to the integral of that property along a closed loop or cycle. If the property being integrated is a conservative property, such as a conservative force or a conservative field, then the cyclic integral will always be zero. This is because a conservative property does not depend on the path taken, only on the initial and final points. Therefore, the correct answer is zero.

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• 18.

### A real gas behaves as an ideal gas when?

• A.

Temperature approaches zero

• B.

Pressure approaches zero

• C.

Both temperature and pressure approaches zero

• D.

None of the mentioned

B. Pressure approaches zero
Explanation
When the pressure approaches zero, a real gas behaves as an ideal gas. This is because at very low pressures, the intermolecular forces between gas molecules become negligible. As a result, the gas molecules occupy a large volume compared to the size of the gas molecules themselves, and they move independently without any significant interactions. This behavior is similar to that of an ideal gas, where the gas molecules are assumed to have no volume and no intermolecular forces.

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• 19.

### Heat is a

• A.

Point function

• B.

Path function

• C.

Depends on the state

• D.

None of the mentioned

A. Point function
Explanation
A point function is a thermodynamic property that depends only on the initial and final states of a system, regardless of the path taken to reach those states. Heat is a point function because it is determined solely by the temperature difference between the initial and final states, and not by the specific process or path used to transfer the heat.

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• 20.

### Equation of continuity comes from

• A.

Conservation of energy

• B.

Conservation of mass

• C.

Conservation of work

• D.

Conservation of heat

B. Conservation of mass
Explanation
The equation of continuity is derived from the principle of conservation of mass. This principle states that mass can neither be created nor destroyed, but only transferred or transformed. In the context of fluid dynamics, the equation of continuity ensures that the mass flow rate remains constant along a streamline. It states that the product of the fluid's cross-sectional area and its velocity is constant, indicating that as the area decreases, the velocity increases to maintain the same mass flow rate. Thus, the equation of continuity is directly derived from the conservation of mass principle.

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• Current Version
• Mar 21, 2023
Quiz Edited by
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• Nov 10, 2019
Quiz Created by
Shailendra Kumar

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