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Kenyatta University Question Paper

Kenyatta University

Course:Bachelor Of Science In Mechanical Engineering

Institution: Kenyatta University question papers

Exam Year:2008

KENYATTA UNIVERSITY
UNIVERSITY EXAMINATIONS 2008/2009
FIRST SEMESTER EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE
SET 211: ENGINEERING MECHANICS 1
INSTRUCTIONS
Attempt any 3 questions.

Question 1
(a) State two conditions which must be met by three forces in the same plane to be in
equilibrium. [1 mark]
(b) Explain the meaning of the terms:-
(i) Parallelogramme of forces
(ii) Polygon of forces [2 marks]
(c) Distinguish between a resultant and equilibrant force. [1 mark]
(d) Find the magnitude, direction and position of the resultant of the system of forces
shown in Figure 1. The forces act at the four corners of a square of 2m side.

Question 2
(a) (i) What is the moment of a force? [1 mark]
(ii) State the principle of moments for a body in static equilibrium.
[2 marks]
(b) Figure 2 shows a link BC which is maintained in equilibrium by three forces at B, G and C. Thereforce at B is along line Y-Y. The force at G is 200N and acts at 45o to the link as shown.
Find
(i) the magnitude of the force at B.
(ii) the magnitude and direction of the force at C; If BG = GC = 500mm.
[6 marks]
(c) (i) Calculate the magnitude and direction of the force at A (fig 3).
[3 marks]
(ii) Determine analytically the magnitude and nature of the forces in bars 1, 2
and 3 in figure 3. All bars are of equal length. [8 marks]

Question 3
(a) State the Parallel Axis Theorem. [1½ marks]
(b) Define the term Radius of gyration. [1½ marks]
(c) Calculate the 2nd moment of area of the T-section shown in fig 4 about a line X-X
through the cutroid parallel to the flange face. [17 marks]

Question 4
(a) Define the term. [1 mark]
(i) Centre of Gravity
(ii) Centroid [1 mark]
(b) Working from First principles, determine the distance y from the base of a
triangle of height h to the centroid of its area. [7 marks]
(c) Determine the coordinate of the cutroid x and the moment of inertia of area Iy of
the parabolic semi-segment shown in figure 5.
The equation of the parabolic boundary of the semi-segment is given by
y=(1-x2/b2) [11 marks]

Question 5
(a) Working from first principles and explaining the meaning of all symbols and
notations used derive an expression for the efficiency of a single-start square
threaded screw when raising a load. [10 marks]
(b) A double-start square threaded screw drives the cutter of a machine tool against
an axial load of 550N. The external diameter of the screw is 52.5mm and the
pitch is 5mm.
(i) If the coefficient of friction for the thread is 0.15, find the torque required
to rotate the screw. [6 marks]
(ii) If the cutting, speed is 120mm/s find the power required at the operating
nut of the screw. [4 marks]

Kenyatta University Question Paper

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