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Sce 215:Mechanical Engineering Principles Question Paper
Sce 215:Mechanical Engineering Principles
Course:Bachelor Of Science In Computer Engineering
Institution: Kenyatta University question papers
Exam Year:2009
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KENYATTA UNIVERSITY
UNIVERSITY EXAMINATIONS 2008/2009
FIRST SEMESTER EXAMINATION FOR THE DEGREE OF BACHELOR OF
SCIENCE (COMPUTER ENGINEERING)
SCE 215: MECHANICAL ENGINEERING PRINCIPLES
DATE: FRIDAY, 28TH NOVEMBER 2008
TIME: 11.00 A.M. – 1.00 P.M.
INSTRUCTIONS:
? Answer question ONE and any other TWO questions.
? You may use the following constants and formula.
Gravitational acceleration, g = 9.81 ms-2
1 bar = 105 pascals
Density of water
3
1000
?
?
kgm
water
Question One (30 marks)
a)
Define the following terms as used in materials:
(i)
Rotational Inertia
(2 marks)
(ii)
Young’s modulus of elasticity
(2 marks)
(iii)
Cantilever
(2 marks)
b)
A lift cage has a mass of 200 kg. Its outside diameter is 1.5 m and moment
of inertia 130 kgm2 . Ignoring the effect of the rope, calculate the total k.e.
in the system when the cage is being raised at a uniform speed of 1.5 ms-1 (3 marks)
c)
A pipe used to carry water is raised at some angle from the horizontal axis.
Water enters the pipe with a pressure of 3 bar and velocity 6 ms-1. The pressure
in the water 30 m below entry point is 1.4 bar, calculate its velocity.
(3 marks)
2
d)
Distinguish between space diagram and force diagram.
(1 mark)
e)
Verify from initial state that the general solution for under damped harmonic
motion is given by x = ce-?t cos(?t-?) where symbols have their usual meanings.
(3 marks)
f)
State three types of gears
(3 marks)
g)
Water of density 1000 kgm-3 enters a horizontal pipeline with a pressure
and velocity of 2 Mpa and 7.5 ms-1 respectively and leaves with pressure
of 1.65 Mpa and velocity 25 ms-1. Determine the loss of head due to frictional
force.
(3 marks)
h)
What is fatigue test on a material?
(2 marks)
i)
Identify two conditions for a body to be in equilibrium.
(2 marks)
j)
What are the two assumptions made in the simple theory of bending?
(2 marks)
k)
Distinguish between angular velocity ratio and pressure angle in gear forces.
(2 marks)
Question two (20 marks)
a)
Write down the equation of power transmitted by a belt drive as a function
of belt tensions and belt speed defining all symbols used.
(4 marks)
b)
A V-belt drive is to transmit 18.5 Kw from a 250 mm pitch diameter sheave
operating at 1800 rev/min to 900 mm diameter flat pulley. The centre
distance between the input and output shafts is 1 m. The groove angle
? = 40o and the coefficient of friction for the belt and sheave is 0.2 and the
coefficient of friction between the belt and flat pulley is 0.2. The cross section
of the belt is b2 = 38 mm wide at the top and b1 = 19 mm wide at bottom by
d = 25 mm deep. Each belt weighs 11 KNm-3 and the allowable tension per
belt is 900 N. How many belts are required?
(16 marks)
Question three (20 marks)
a)
Distinguish between a strut and a tie in girders.
(2 marks)
3
b)
Determine the forces acting on each member of the truss shown in figure 1.
The ends of the truss rest on a smooth surface.
(18 marks)
Figure 1
Question four (20 marks)
a)
Distinguish between free harmonic vibration and forced harmonic vibration.
(3 marks)
b)
A particle of mass 5 kg moves along the x-axis under the influence of two
forces (i) a force of attraction to origin O which in Newtons is numerically
equal to 40 times the instantaneous distance from O and (ii) a damping force
proportional to the instantaneous speed such that when speed is 10 ms-1, the
damping force is 20 m from O,
(i)
set up the differential equation and conditions describing the motion.
(6 marks)
(ii)
find the position of the particle at any time.
(3 marks)
(iii)
determine the amplitude, period and frequency of the damped
oscillations.
(6 marks)
(iv)
graph the motion.
(2 marks)
Question five (20 marks)
a)
Briefly explain the reasons for lubricating parts of a machine.
(2 marks)
b)
Identify two items which may influence the strength of a machine member.
(2 marks)
4
c)
A hollow shaft of external diameter 50 mm and bore 35 mm is to transmit
a torque of 70 Nm. If the shaft is 0.8 m long and shear modulus is 80 GNm-2,
determine:
(i)
the maximum shear stress
(4 marks)
(ii)
the maximum angle of twist
(4 marks)
d)
An experimental which disc flywheel has a mass of 120 kg and an outside
diameter of 300 mm. With the flywheel at rest, a constant torque of
10 Nm is applied for a period of 2 seconds. Ignoring the effect of friction,
determine:
(i)
the moment of inertia
(3 marks)
(ii)
the angular acceleration
(2 marks)
(iii)
the angular velocity after 2 seconds
(3 marks)
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