Quiz: Mechanical Engineering 6th July

Quiz: Mechanical Engineering
Exam: AE/JE
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/4 mark
Time: 10 Minutes

Q1. The length of the links of a 4-bar linkage with revolute pairs only are p, q, r and s units. Given that p<q<r<s. Which of these links should be the fixed one, for obtaining a ‘double crank’ mechanism?
(a) Links of length p
(b) Links of length q
(c) Link of length r
(d) Link of length s

Q2. According to Kennedy’s theorem, the instantaneous centres of three bodies having relative motion lie on a
(a) curved path
(b) straight line
(c) point
(d) approximate straight line

Q3. A satellite float in deep space with very high velocity. It will continuously lose heat by
(a) convection
(b) conduction and convection
(c) radiation
(d) radiation and convection

Q4. Consider the following statements:

1. The thermal conductivity of a material is its ability to conduct heat
2. The thermal conductivity can be defined as the rate of heat transfer through a unit
   thickness of the material per unit area.
3. In solids, heat conduction is due to lattice vibrational energy as well as energy
   transported via free flow of electrons.
4. Convection involves combined effect of conduction and fluid motion.
   Which of the above statements are valid?
   (a) 1 and 2
   (b) 2, 3 and 4
   (c) 1, 3 and 4
   (d) 3 and 4

Q5. The equation,δQ=dU+PdV,is true for
(a) any system, any process
(b) any system, reversible process
(c) closed system, any process
(d) closed system, only reversible process

Q6. Energy tends over to gravitate to a lower degree of intensity so long as it undergoes no transformation.
Which law of thermodynamics is related to this statement?
(a) Zeroth law
(b) First law
(c) Second law
(d) Third law

Q7. One kg of water at room temperature is brought into contact with a high temperature thermal reservoir. The entropy change of the universe is
(a) equal to entropy change of the reservoir
(b) equal to entropy change of water
(c) equal to zero
(d) always positive

Q8. The tendency of knocking in diesel engine reduced by
(a) high self-ignition temperature of fuel
(b) decrease in jacket water temperature
(c) injection of fuel just before TDC
(d) decrease in injection pressure

Q9. In CI engines by increasing inlet air pressure, the knocking tendency
(a) increases
(b) decreases
(c) not affected
(d) first decreases and then increases

Q10. Which of the following feature(s) is/are used in the combustion chamber design to reduce SI engine knock?
(a) Spark plug located away from exhaust valve wedge shaped combustion chamber and short flame travel distance
(b) Wedge shaped combustion chamber
(c) Wedge shaped combustion chamber and short flame travel distance
(d) Spark plug located away from exhaust valve, short flame travel distance and side valve design

Solutions
S1. Ans (a)
Sol.
Grashoff’s Law- It is valid for four bar linkage.
Class-I four bar linkage
(S+l)≤(a+b) S→ shortest link
l→ Longest link
Class-II four bar linkage a, b → other links
(S+l)> (a+b)
For class-I
If shortest link (s) is fixed then we obtain double crank Mechanism.
If link opposite to shortest link (s) is fixed then we obtain double rocker Mechanism
If link other than shortest or opposite to shortest link is fixed then we obtain crank- rocker Mechanism.
For class-II
By fixing any link, we obtain double rocker Mechanism.

S2. Ans (b)
Sol.
Kennedy’s theorem states that when three links are in relative motion then the I – center of three links will lie on the same line.
e.g. – I_12,I_23,I_13 lies on the same line in the above figure.

S3. Ans (c)
Sol. As there is no medium in space for conduction and convection heat transfer to take place, hence heat can be continuously lost by radiation heat transfer.

S4. Ans (c)
Sol. Thermal conductivity of a material is its ability to conduct heat and can be defined as the rate of heat transfer for unit change of temperature from unit thickness per unit area. Conduction in solid is a combination of lattice vibration and electron motion. Convection heat transfer takes place through combined effect of conduction and motion of fluid.

S5. Ans (d)
Sol. As given equation consists of PdV (or displacement) work, which is valid only for closed system and this equation consists of point functions as well as path functions. So, this equation
δQ=dU+PdV , is valid for closed system and only reversible process.

S6. Ans (c)
Sol. Second law of thermodynamics is also known as law of degradation of energy.

S7. Ans (d)
Sol. Entropy of universe (or isolated system) always increases or remains constant.

S8. Ans (c)
Sol. If we inject fuel in diesel engine, just before TDC then knocking tendency will decrease due to high temperature of surrounding and hence, instant ignition of fuel.

S9. Ans (b)
Sol. By increasing the inlet air pressure, atomization of fuel is better that helps the fuel to ignite easily. Hence, it reduces knocking tendency in the CI engine.

S10. Ans (c)
Sol. Spark plug should be located near the exhaust valve, so that it will not in the end charge region otherwise knocking will occur. Wedge shaped combustion chamber and short flame travel distance are also the features of combustion chamber to reduce knock in the SI engine.

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