West Bengal Institute of Technology (WBIT) 2010-1st Year B.Tech Electronics and Communications Engineering WBUT Mechanical Science - Question Paper
CS/B.Tech/SEM-2/ME-201/2010
Mechanical Science
Time Allotted : three Hours
Full Marks : 70
Name:. ....................................... RollNo. : ..Q$QG$Otg...........................
Invigilators Signal :ure : ..........
CS7S.TECH/sIm2/ME-201/2010 2010 MECHANICAL SCIENCE
Time Allotted : 3 Hours Full Marks : 70
The.* figures in the margin indicate full rncj'ks.
Candidates a ire required to give their answers in their own words
as far as practicable.
GROUP - A ( Multiple Choice Tye gestions )
1. Choosf * the correct alternatives for the following :
10 x 1 10
i) 'The study of thermodynamics provides answer to the following, except
a) whether a process is feasible or not
b) how much energy is required for a process to take pi act:
c) rate or speed with which a process occurs
d) extent to which a reaction/process takes place,
ii1] r or an irreversible process entropy change is
a) greater than b) equal to
c) less than d) equal to zero.
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iii) The work done in a steady flow proc 'ess is given by a) Jpdu b) J - iidv
iv) Extensive property of a system is one v /h ose value
a) depends on mass of the system
b) is independent of mass of the system n
c) is always constant
d) is dependent on the paih followed , not on the state.
v) Idea of temperature scale is obtained from
a) Zeroth law of Thermodynamics
b) First law of Thermodynamics
c) Second lav? of Thermodynamics
d) none of these.
vi) A stagnation point is a point in a fluid where
a) total energy is zero
b) velocity of the flow is zero
c) total ennergy is maximum
d) pressue is zero.
vii) A pitot tube is used for the measurement of
a) flow b) pressure
c) discharge d) velocity.
viii) Streamline is a iii ie
a) which is alon* % the path of particle
b) which is alwa ys parallel to the main direction of flow
c) across which tli ere is no flow
d) on which a tang ent drawn at any point gives the direction of veloeii ty.
ix) Stroke is the unit of
a) Surface tension b) Dynamic viscosity
c) Kinematic viscosity d) none of these.
x) Absolute pressure can be obtaixied from a pressure gauge,
gauge + atm gauge atm
gauge X atm gauge ? aim '
GKOUP-B ( Short Aiissr Type Questions )
Answer any three of the followi ng. 3x5= 15
2. The fhuid flow is given by V- x2 yi+ y2 zj - (2xyz + yz2) k. Show t hat this is the case of possible steady incompressible flow. Calculate the velocity and acceleration at ( 2, 1, 3 ).
3, A 150 mm diameter shaft rotates at 1500 r.p.m. in a 200 mm long journal bearing with an internal diameter 150*5 mm- The uniform annular space between the shaft and the t >earing is filled with oil of dynamic: viscosity
' 0*8 poise. Calculate the power required to rotate th e shaft.
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4. A gaseous system undergoes three quasi-static processes in sequence. The gas initially at 5 b? ar & 0*01 m3 is expanded at constant pressure. It is then f urther expanded according to the relation PV2 = C to 2 b ar & 0-025 ra3, The gas is then returned to its initial s t.ate during which process PV=C. _
i) Sketch the cycle in the F V plane__
ii) Calculate the net work for the system. 2 + 3
5. State the 2nd law of th .ermoiiynainics. Show that the efficiency of a reversible e? j.gine operating between two given constant temperatures is fi7ne maximum. 2+3
6. Classify various types c fluid with the help of Rheologioal diagram.
CvROUP - C ( Lozsg Answer Type Questions )
Answer any three of the following. 3x175 = 45
7. a) a revejsible heat engine takes in heat from a reservoir
at S40C a nd rejects heat to a reservoir at 60/C. The heat engine drives a reversible heat pump whf* ch takes in heat '/rom a reservoir at 5C and delivers . heat to a reservoir at 60C. The reversible heat engine also drives the machine that absorbs 30 kW. fj the heat pump extracts 17 kJ/s from a 5C reservoijr, determine
i) the rate of heat supply from 840C sc arce
ii) the rate of heat rejection to 60C sinJk.
b) Calculate the entropy change of 1 kg of water at 27C, when it is converted to ice at - 20 C. Specific heats oi ice and water are 2*18 kJ/kg-K and 4-18kJ/kg-K respectively and latent heat of fusion of ice at 0C is 335 kJ/kg. 10 + 5
8. a) What is an air standard cycle ? Derive an expression
for the efficiency of a diesel cycle.
b) In a diesel engine, the compression ratio is 13 : 1 and the fuel is out off at of the stroke. Find the air standard efficiency of 4he engine. Take y of air = 1-4.
9 + 6
9. a) Why does the viscosity of a gas increase with the
increase in temperature while that of a liquid decrease with increase in temperature ?
b) The space between two large flat and parallel walls, 25 mra apart is filled with a liquid of absolute viscosity of*7 N-s/m2. Within this space, a thin flat plate 250 mm x 250 mm is towed at a velocity of 150 mm/s at a distance of 6 mm from one wall, the plate and its movement being parallel to the walls. Assuming linear variations of velocity between the plate and the walls, determine the force exerted by the liquid on the plate.
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c) What is flowing through two different pipes to which an inverted differential manometer having an oil of sp. gr, 0-8 is connected. The pressure head in the pipe A is
2 m of water. Find the pressure in pipe B for the manometer readings as shown in figure below.
2 + 6 + 7
What is orifice meter ? Prove that the discharge through the orifice meter is given by the relation
10. a)
o \>s/ ) a n a
V2 gh
Q =
where a x is area of the pipe orifice meter fitted, a0 is the area of the orifice.
b) What is Euler's equation of motion. Prove the Eulers equation of motion. How you can obtain the Bernoullis equation from it ? 2 + 6 + 7
A mass of air is initially at 260C and 700 kPa and occupies 0-028 m3. The air is expanded at constant pressure to 0*084 m3. A polytropic process PV1,5 is then carried out followed by a constant temperature process which completes the cycle. All the processes are reversible. Find the efficiency of the cycle.
State first law of Thermodynamics for ft closed system undergoing a cycle. Why is the value of specific heat at constant pressure greater than specific heat at constant volume ? 12 + 3
b)
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