CE 10224A - Science for CE (Physics)

Question 1

What are the 2 branches of dynamics?

Answer 1

• Kinematics (the study of the motion of point masses or rigid bodies. Focuses on calculating position, displacement, velocity and acceleration (not the forces causing them)
• Kinetics (the study of the forces that produce or change motion)

Question 2

What are the types of friction?

Answer 2

Static frictional force, Fs - the force, opposing direction of motion and resulting in a static condition.

Kinetic friction, Fk - frictional force opposing motion as the object is moving.

Question 3

How is static friction calculated?

Answer 3

𝐹𝑠 = 𝜇s𝐹Ν

Where:

Fs is static friction
𝜇s is coefficient of static friction
FN is the normal force

Question 4

How is kinetic friction calculated?

Answer 4

𝐹𝑘 = 𝜇k𝐹N

Where:

Fk is kinetic friction
𝜇k is coefficient of kinetic friction
FN is the normal force

Question 5

In terms of friction coefficient, what causes an object to remain stationary?

Answer 5

When kinetic frictional force is less than force of static friction.

Question 6

How is drag force calculated?

Answer 6

𝐷 = 1/2𝐶𝜌𝐴𝑣^2

Where:
D is drag force
C is the drag coefficient
𝜌 is fluid density
A is cross-sectional surface area perpendicular to v
v is fluid velocity

Question 7

How is centripetal force calculated?

Answer 7

𝑭𝒄 = 𝒎𝒗𝟐 / 𝒓

Question 8

How is velocity and angular velocity calculated?

Answer 8

𝑣 = 2𝜋𝑟 / 𝑇

𝑣 = 2𝜋𝑟𝑓

𝑣 = 𝜔𝑟

𝜔 = 2𝜋 / 𝑇

Question 9

How is centripetal acceleration calculated?

Answer 9

𝒂𝒄 = 𝝎^𝟐𝑟

𝒂𝒄 =𝒗^𝟐 / 𝒓

Question 10

How are forces analysed in non-uniform circular motion?

Answer 10

If 𝐹𝑡𝑜𝑡 is acting at an angle, then this force causes a non-uniform circular motion

Analysis into x, y-axis components:

• There’s a force directed towards the centre of the circle causing the centripetal acceleration, 𝒂𝒄
• A tangential force causes a tangential acceleration called 𝒂𝒕𝒂𝒏.

These accelerations are perpendicular to one another.

Question 11

For non - uniform circular motion, how is total acceleration and angular acceleration calculated?

Answer 11

𝒂𝒄 = 𝝎^𝟐𝑟

𝒂𝒕𝒂𝒏 = 𝒅𝒗/𝒅𝒕 = 𝑟 𝒅𝝎/𝒅𝒕

𝒂𝒕𝒐𝒕 = (𝒂𝒄^2 𝟐+𝒂𝒕𝒂𝒏^2)^1/2

𝒂𝒂𝒏𝒈= 𝒅𝝎/𝒅𝒕
= (𝝎𝟐−𝝎𝟏) / (𝒕𝟐−𝒕𝟏)

Question 12

How are angular and tangential accelerations related?

Answer 12

𝒂𝒕𝒂𝒏 = 𝑟*𝒂 𝒂𝒏𝒈

Question 13

What’s centrifugal force?

Answer 13

Ff, a ‘’ reactive’’ force acting upon a body due to rotation, and on the opposite direction of the centripetal force, at an equal magnitude, away from the centre of rotation.

Question 14

What’s ‘’apparent’’ centrifugal force?

Answer 14

Fapp, a force which pushes the object away from the centre of rotation.
This is not part of any interaction, but it is the objects inertia.

Question 15

How is work done calculated?

Answer 15

𝑊 = 𝐹𝑐𝑜𝑠𝜃(𝑥𝐵 − 𝑥𝐴)

𝑊 = 𝑃(𝑉2 − 𝑉1)

Question 16

How is gravitational potential energy calculated?

Answer 16

[E = mgh]

U = mg(h2-h1)

Question 17

How is kinetic energy calculated?

Answer 17

E = mv^2/2