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1.
Consider a PERT network for a project involving six tasks (a to f).
Task
Predecessor
Expected task time (in days)
Variance of the task time (in days2 )
a
-
30
25
b
a
40
64
c
a
60
81
d
b
25
9
e
b,c
45
36
f
d,e
20
9
[1] The expected completion time of the project is: [2 marks]
(A) 238 days
(B) 224 days
(C) 171 days
(D) 155 days[2] The standard deviation of the critical path of the project is: [2 marks]
(A) √151 days
(B) √155 days
(C) √200 days
(D) √238 daysasked in Mechanical Engineering, 2006
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2.
A smooth flat plate with a sharp leading edge is placed along a gas stream flowing at U=10 m/s. The thickness of the boundary layer at section r − s is 10 mm, the breadth of
the plate is 1 m (into the paper) and the density of the gas ρ = 1.0 kg/m3. Assume that the boundary layer is thin, two-dimensional, and follows a linear velocity distribution,
u = U (y/δ ) , at the section r − s , where y is the height from plate.
[1] The mass flow rate (in kg/s) across the section q − r is: [2 marks]
(A) zero
(B) 0.05
(C) 0.10
(D) 0.15[2] The integrated drag force (in N) on the plate, between p − s , is: [2 marks]
(A) 0.67
(B) 0.33
(C) 0.17
(D) zeroasked in Mechanical Engineering, 2006
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3.
A football was inflated to a gauge pressure of 1 bar when the ambient temperature was 15°C. When the game started next day, the air temperature at the stadium was 5°C. Assume that the volume of the football remains constant at 2500 cm3.
[1] The amount of heat lost by the air in the football and the gauge pressure of air in the football at the stadium respectively equal [2 marks]
(A) 30.6 J, 1.94 bar
(B) 21.8 J, 0.93 bar
(C) 61.1 J, 1.94 bar
(D) 43.7 J, 0.93 bar[2] Gauge pressure of air to which the ball must have been originally inflated so that it would equal 1 bar gauge at the stadium is: [2 marks]
(A) 2.23 bar
(B) 1.94 bar
(C) 1.07 bar
(D) 1.00 barasked in Mechanical Engineering, 2006
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4.
A vibratory system consists of a mass 12.5 kg, a spring of stiffness 1000 N/m, and a dashpot with damping coefficient of 15 Ns/m.
[1] The value of critical damping of the system is: [2 marks]
(A) 0.223 Ns/m
(B) 17.88 Ns/m
(C) 71.4 Ns/m
(D) 223.6 Ns/m[2] The value of logarithmic decrement is: [2 marks]
(A) 1.35
(B) 1.32
(C) 0.68
(D) 0.66asked in Mechanical Engineering, 2006
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5.
A simply supported beam of span length 6 m and 75 mm diameter carries a uniformly distributed load of 1.5 kN/m.
[1] What is the maximum value of bending moment? [2 marks]
(A) 9 kNm
(B) 13.5 kNm
(C) 81 kNm
(D) 125 kNm[2] What is the maximum value of bending stress? [2 marks]
(A) 162.98 MPa
(B) 325.95 MPa
(C) 625.95 MPa
(D) 651.90 MPaasked in Mechanical Engineering, 2006
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6.
A planetary gear train has four gears and one carrier. Angular velocities of the gears are w1 , w2, w3 and w4 respectively.The carrier rotates with angular velocity w5.
[1] What is the relation between the angular velocities of Gear 1 and Gear 4? [2 marks]
(A) (w1 -w5 )/(w4 -w5)=6
(B) (w4 -w5 )/(w1 -w5)=6
(C) (w1 -w2 )/(w4 -w3)=-2/3
(D) (w2 -w5 )/(w4 -w5)=8/9[2] For w1 = 60 rpm clockwise (cw) when looked from the left, what is the angular velocity of the carrier and its direction so that Gear 4 rotates in counterclockwise (ccw) direction at twice the angular velocity of Gear 1 when looked from the left [2 marks]
(A) 130 rpm, cw
(B) 223 prm, ccw
(C) 256 rpm, cw
(D) 156 rpm, ccw
asked in Mechanical Engineering, 2006
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