Info on Final Exam

8/12/2019 Info on Final Exam

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Race Day

Date : 04 JUNE 2013 (TUESDAY)

Venue : 6th Floor (Green Building)

Tentative : 9.00 am – Collect your car from DrRoszaidi

9.30 am – the race start

+++ At least one group member shall attend the

race +++



BMCM 2713 DYNAMICS

SEM 2 2012 2013

SOME INFO ON THE FINAL EXAM



Number of Questions to be

answered…?

You need to answer 4 questions in totatl which

consists of:

• Q1 and Q2 (These two questions are

compulsory)

• Any 2 Questions from Q3, Q4 and Q5



Q1

• Chapter 4: Kinetics of a Particle: Impulse and

momentum

• Purely calculation

• Divided into Q1(a) – 10 marks and Q1(b) – 15

marks

•

Give more attention to central impact andoblique impact.



Q2

Chapter 5: Planar Kinematics of a Rigid Body• Purely calculation

• Divided into Q2(a) – 10 marks and Q2(b) – 15 marks

• Give more attention to rotation about a fixed axis for Q2(a). Be sure you knowthe characteristics of the rectilinear and angular coordinates/parameters ofthe two cases below.

• Relative motion analysis (acceleration) Q2(b).



Q3, Q4 and Q5

1. You need to know the moment of inertia ofcommon shapes such as rod, sphere, ring,cylinder, disk etc. These are not given in the

exam.2. These questions consist of two parts:

a) Descriptive (10 marks) – you need to explain thereason to your answer based on the concepts you

learnt from the subject. In some question it mayrequire minor calculation.

b) Calculation (15 marks)



Q3

Chapter 6: Planar Kinetics of a Rigid Body: Force

and Acceleration

• Need to understand the term “rolls without

slipping”

• For the descriptive question – focus on the

general plane motion of the rolling bodies

• For the calculation question – focus on the

general plain motion of a rod



Q4

Chapter 7: Planar Kinetics of a Rigid Body: Work

and Energy

• Descriptive question – remember to relate

your answer to either principle of work and

energy, and conservation of energy

• Calculation question – focus of the principle of

work and energy – be careful on the work

done by a couple moment.



Q5

Chapter 8: Planar Kinetics of a Rigid Body:

Impulse and Momentum

• Descriptive question – relate your answer to

either principle of angular impulse and

momentum or conservation of angular

momentum.

• Calculation question – general plane motion

of a rolling body.



Some examples/ideas on the

descriptive questions

Chapter 6• Define the moment of inertia. Explain briefly the concept of parallel axis

theorem.

• Explain briefly how the parallel-axis theorem can be used in determining

the rotational equation of motion for the unbalanced flywheel shown in

the figure, where G is the centre of gravity of the flywheel.



Chapter 6

• A farmer is trying to lift a 300 kg cow from the edge of a cliff at a constantspeed. He is thinking of using two methods shown in the figure. The firstmechanism consists of a frictionless fixed pulley at A while the secondmechanism consists of a fixed frictionless pulley at A and a movable pulleyat B. Compare the performance of the two methods in terms of the total

time taken and the force that is needed in order to lift the cow. Supportyour answer with a simple theoretical analysis. Detail calculation is notnecessary.

A

B

C



Chapter 6• Explain briefly the term kinetic moment in the equation of rotational motion of a

rigid body.• The sphere, cylinder and thin ring shown in the figure below each have mass m

and radius r . Each is released from rest on identical inclines. Assuming that theyroll without slipping, determine which body will have the largest initial angularacceleration by using the method of force and acceleration?

OG

Gr

y

x

θ

y

x

θ

y

x

θ

G G G

Thin ring Solid cylinder Solid sphere

2

G I mr =21

2G

I mr =22

5G

I mr =

r r r

• The unbalanced flywheel shown in the figure is free to rotate about point O. Writedown the rotational equation of motion for the unbalanced flywheel both about

point O and G, where G is the centre of gravity of the flywheel.



Chapter 7

• With the aid of a diagram, explain why the weight of an

object is a conservative force.

• Derive the expression for the principle of work and energy.

• What is the main different in work and energy methods when they

are applied to problems involving rigid bodies as opposed to whenthey are applied to problems involving particles?

• There are some external forces that do no work when the body is

displaced. Give two examples of these forces and explain why these

forces do no work.



Chapter 7

• A single badminton player is planning to buy a new racket. The racket, asshown in the figure, is normally categorized according to the weight of thehead (head heavy or head light) and the flexibility of the shaft (flexible orstiff). As a single player, he is aiming for a racket which can provide amassive power and a good accuracy. As a sale person, which of the headand shaft criteria would you suggest to the player? Explain and relate you

answer to the concept of mechanical energy. No detail calculation isnecessary.



Chapter 7

• Three rigid bodies shown in the figure (a thin ring, a solid cylinder and a solid

sphere) have the same radius r and mass m. They are released from rest at the

same elevation and at the same instant. They roll without slipping down the

identical planes for a distance x = 1 m. Using the principle of conservation of

energy, determine which body first travels the 1 m distance. Based on your

answer, conclude the meaning of the term mass moment of inertia?

y

x

θ

y

x

θ

y

x

θ

G G G

Thin ring Solid cylinder Solid sphere

2

G I mr =

21

2G

I mr =22

5G

I mr =

r r r



Chapter 8

• Derive the expression for the principle of impulse and momentum.

• What is an impulsive force? Explain briefly the importance of the car

bumper in the context of impulse and momentum.

• From momentum and impulse perspective, explain why a car is designed

in such a way that it will experience damage easily during an accident or acrash.

• Define

o Linear momentum

o Angular momentum

•

Consider a swimmer who executes a somersault after jumping off a divingboard. The swimmer first tucks in his arms and legs close to his chest, then

straightens out just before entering the water. Explain why he does that

using the concept from the principle of angular impulse and momentum.



Chapter 8

• Spins are common in ice-skating. In a spin, a skater rotates about a

vertical axis that runs through the skater’s body. The skater controls

his spin rate by extending or retracting the arms and/or legs.

Explain how the skater is able to control the spin without external

help. Relate your answer to the principle of conservation of angularmomentum.

• From momentum point of view, explain why a baseball bat is

designed with very solid and strong structure.

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Info on Final Exam