.
CONFIDENTIAL
UTHM
Universiti Tun Hussein Onn Malaysia
UNIVERSITI TUN HUSSEIN ONN MALAYSIA
FINAL EXAMINATION
SEMESTER
sEsr
I
2015t201,6
COURSE NAME
:
MECHANICS OF MACHINES
COURSE CODE
:
BNJ 20303
PROGRAMME
:
4 BNH/BNL
DATE
DURATION
:
:
DECEMBER 2015/JANUARY 2016
TNSTRUCTION
:
ANSWER FIVE (5) QUESTIONS
ONLY
EXAMINATION
3 HOURS
THIS QUESTION PAPER CONSISTS OF EIGHT (8) PAGES
CONFIDENTIAL
CONFIDENTIAL
Ql
BNJ 20303
(a)
Explain briefly about velocity ratio, slip and discuss the effect of belt thickness and
slip on velocity ratio.
(5 marks)
(b)
The slack side of the belt drive is preferable to place on the top side as shown in
FIGURE Ql(b). Discuss the possible reason behind this.
(3 marks)
(c)
An open belt drives connects two pulleys 120 cm and 50 cm diameter, on parallel
shafts 4 metres apart. The mass of belt per metre length is 0.9 kg and maximum
tension is not to exceed 2000 N. The coefficient of friction is 0.3. The 120 cm pulley,
which is the driver, runs at 200 rpm. Because of belt slip on one of the pulleys, the
velocity of the driven shaft is only 450 rpm. Calculate,
(i)
The torque on each of the two shafts.
(6 marks)
(iD The power transmitted.
(2 marks)
(iii) The power lost in friction.
(2 marks)
(iv)
What is the efficiency of the drive?
(2 marks)
Q2
(a)
(b)
Gear system is used in power transmission system for most of the mechanical
system nowadays. Gear can be classified according to the relative position of the axes
of the mating gears. Describe AND give ONE (1) example, the types of axes of the
mating gears.
(5 marks)
has a mass of 1000 kg carries a load of mass Mkg, moves directed at an
angle 15" using the first gear. The wheels run at 400 rpm when the engine speeds at
2000 rpm. The moment of inertia of the wheel is 20 kgrn' and the engine part is 2
kgm'. The wheel has a radius of 0.5m and the engine can produce maximum torque of
600 Nm.
A vehicle
Determine :-
(i)
(ii)
Gear ratio for the first gear.
The maximum value of M if the vehicle climbs up with 0.5m/s2
acceleration. Assuming wind friction is 250 N and gear efficiency is
90o/o.
(I
5 marks)
CONFIDENTIAL
CONFIDENTIAL
Q3
(a)
BNJ 20303
The pitch of 50 mm mean diameter threaded screw of a screw jack is 12.5 mm. The
coefficient of friction between the screw and the nut is 0.13. Determine the torque
required on the screw to raise a load of 25 kN, assuming the load to rotate with the
screw.
(i)
Determine the ratio of the torque required to raise the load to the torque
required to lower the load.
(5 marks)
(ii)
Determine the efficiency of the machine.
(5 marks)
(b)
A plate clutch
has three discs on the driving shaft and two discs on the driven shaft,
providing four pairs of contact surfaces. The outside diameter of the contact surfaces
is 240 mm and inside diameter 120 mm. Assuming uniform pressure and coefficient
friction, p: 0.3;
(i)
Determine the total spring load pressing the plates together to transmit 25 kW
at 1575 r.p.m.
(5 marks)
(ii) If there are 6 springs each of stiffness 13 kN/m and each of the contact
surfaces has worn away by I.25 hffi, determine the maximum power that can
be transmitted, assuming uniform wear.
(5 marks)
Q4
(a)
Describe briefly about balancing technique for machine or rotatinh mechanical part
AND explain how it is said to be perfectly balanced..
(3 marks)
(b)
A
shaft carries four rotating masses A, B, C and D in this order, along its axis as
shown in Figure Q4(a) and Figure Q4(b). The mass A is assumed to be concentrated
at a radius of 18 cm, B at24 cm, C at12 cm and D at 15 cm. The masses of B, C and
D are 30kg, 50 kg and 40 kg respectively. The planes containing B and C are 30 cm
apart. The angular spacing of the planes containing C and D are 90o and 210o,
respectively relative to B measured in the same sense. If the shaft and masses are to
be in complete dynamic balance.
Calculate :The magnitude of mass A
The angular position of mass A from B.
The position of the planes A and D from B.
(i)
(ii)
(iii)
(17 marks)
CONFIDENTIAL
CONFIDENTIAL
Qs
BNJ 20303
A mass-pulley-spring
system is shown in Figure Q5. Springs in series and parallel
arrangement are attached to Pulley I and Pulley 2 respectively. The friction and the masses
of the pulley are neglected.
(a)
Draw an equivalent mass-pulley-spring anangement for the system.
(5 marks)
(b)
Draw the free body diagram for the equivalent system.
(5 marks)
(c)
Derive the equation of motion of the system.
(5 marks)
(d)
Calculate the natural frequency of the system if
k:100 N/m andm:5
kg.
(5 marks)
Q6 (a)
A uniform thin rod, ,4^B shown an oscillation system as in Figure 6(a), has a mass of
M at point ^8. The rod is hinged at A and is maintained in the horizontal position by a
spring of stiffness K. The mass .B is supported by a damper with the damping
coefficient is C. Given also a:(l/3)b.
(i)
Find the mass in the oscillation system . (fips
concept and also sketch the diagram)
:
Using the equivalence of mass
(2 marks)
(ii)
Find the damping coefficient in the oscillation system. Qips : Using the
equivalence of damping cofficient concept and also sketch the diagram).
(2 marks)
(iii)
Find damped natural frequency of oscillation system. (fips : Solutions relates
to naturalfrequency, damping ratio and critical damping cofficient).
(4 marks)
CONFIDENTIAL
CONFIDENTIAL
(b)
BNJ 20303
Figure Q6(b) shows an oscillation system of a structure ABDE having a mass 2.5 kg
with radius of gyration of 50 mm about D. Given also a mass atB,8 kg with radius of
gyration about D, 65 mm and another extra mass at the damper , Mp : 0.5 kg.
Consider the system has a pendulum effect,
(i)
Find the natural frequency. (Tips : Using the second Newton's Low that
relates the moment about D and sketch the action offorces at minimum and
maximum position).
(7 marks)
(ii)
From (i), the amplitude was reduced to HALF (%) after THREE (3) complete
oscillations. Find the damping ratio, coefficient damping ratio, critical
coefficient damping ratio and damped natural frequency.
Given the logarithmic decrement
: *(l\=0
\*, )
,
lD"!
,ll-€'
(5 marks)
- EflD oF QUESTION
-
CONFIDENTIAL
CONFIDENTIAL
BNJ 20303
FINAL EXAMINATION
SEMESTER / SESI : SEM II I 201512016
PROGRAMME
COURSE NAME : MECHANICS OF MACHINES COURSE CODE
:
:
4 BNH/4BNL
BNJ 20303
Driven pulley
Driver pulley
FTGURE Ql(b)
A
i-"-* tr'*--fi,| g0 Gmh*-
|
f'+*tr--4,{
FIGURE Q4(a)
CONFIDENTIAL
CONFIDENTIAL
BNr 20303
F'INAL EXAMINATION
SEMESTER / SESI : SEM II I 201512016
PROGRAMME
COURSE NAME : MECHANICS OF MACHINES COURSE CODE
:
:
4BNH/4BNL
BNJ 20303
kg
FIGURE O4ft)
Pulley 2
Pulley
I
FIGTJRE Q5
CONFIDENTIAL
CONFIDENTIAL
BNJ 20303
F'INAL EXAMINATION
SEMESTER / SESI : SEM II I 201512016
PROGRAM : 4 BNH/4BNL
COURSE NAME : MECHANICS OF MACHINES COURSE CODE : BNJ 20303
Mass of 1 kg
200 mm
400 mm
FIGURE O6(a)
K:
M:8kg
mp:O.5 kg
5 kN/m
FIGURE O6ft)
CONFIDENTIAL