Section 3 - Physics

Question 1

Displacement

Answer 1

The distance between the final position and the initial position of an object.

Question 2

Velocity

Answer 2

The rate of change of displacement with respects to time

a = v/t

v = a x t

m/s and miles/hour

Question 3

Acceleration (a)

Answer 3

The rate of change of the velocity (v) with respect to time (t)

a = v/t

m/s²

Question 4

How do you determine the displacement from a graph?

Answer 4

Take the area under the graph or curve.

Question 5

Average acceleration (a_v)

Answer 5

Measures the result of the increase in the speed divided by the time difference

a_v = v^’ - v / /_\t

Question 6

The total displacement of the uniformly accelerated motion is given by the following formula…

Answer 6

x = x₀ + V₀t + 1/2at²

• x₀ = displacement due to the initial displacement x₀
• v₀t = displacement due to the initial velocity v₀ st time t
• 1/2at² = displacement due to the acceleration at time t

Question 7

Equations of kinematics

(The study of objects in motion with respect to space and time)

Answer 7

v = v₀ + at

and

v² = v₀² + 2ax

Question 8

Mass (m)

Answer 8

Its measure of inertia

The centre of mass (COM) of an object always has the simplest motion of all the points of that object

The centre of gravity (COG) is also the centre of mass

W = m x g

m = W / g

Question 9

Weight (W)

Answer 9

Is a force. A vector.

W = m x g

Question 10

Newtons Second law

Answer 10

The sum of all the exterior forces acting upon the centre of mass of a system is equal to the product of the mass of the system by the acceleration of its centre of mass

ΣF = m x a

Question 11

Newton’s Third Law

Answer 11

For every action, there is an equal opposite reaction.

Question 12

The Law of Gravitation

Answer 12

There is a force of attraction existing between any two bodies of masses m₁ and m₂

F = K_G (m₁m₂/r²)

K_G = the universal constant of gravitation

r = distance between the bodies

Question 13

Centripetal Force

Answer 13

• A force that acts on a body moving in a circular path and is directed towards the centre of which the body is moving
• According to Newton’s Second Law, every accelerated particle must have a force acting on it. Thus we can calculate the centripetal force.

F_c = ma_c = mv²/r

• F_c = centripetal force
• a_c = centripetal acceleration
• The magnitude of the acceleration (a_c) is given by v²/r
• r = radius of the circle

Question 14

Acceleration

Answer 14

v = a x t

a = v/t

F = m x a

a = f/m

Question 15

Circumference and Area of a Circle

Answer 15

• Circumference = 2πr
• Area = πr²

Question 16

Torque

• Definitions
• Equations

Answer 16

• Torque (L) is like a turning force. Torque can be defined as the force applied multiplied by the perpendicular distance from the pivot point (= lever or moment arm = r)

L = (force) x (lever arm)

L₁ = F₁ x r₁ = counterclockwise torque (1) = positive

L₂ = F₂ x r₂ = clockwise torque (2) = negative

Question 17

Newton’s First Law

Answer 17

Objects in motion or at rest tend to remain as such unless acted upon by an outside force. That is object have inertia.

Question 18

Inertia

Answer 18

• Resistance to motion
• For translational motion, the mass (m) is a measure of inertia
• For rotational motion, a quantity derived from the mass called the moment of inertia (I) is the measure of inertia

I = Σmr²

r = distance from the axis of rotation

Question 19

Equations for Momentum

Answer 19

M = m v

• M = momentum

Question 20

Equation for Impulse

Answer 20

• The impulse (I) is a measure of the change of the momentum of an object. It is the product of the force applied by the time during which the force was applied to change the momentum

I = F /_\t = /_\M

• F = acting force
• /_\t = elapsed time during which the force was acting

Question 21

Work

• Define
• Equation
• Units

Answer 21

The work on a force F on an object is the product of the force by the distance travelled

Units: 1 joule (J) = 1 N x 1 m

W = F d

Question 22

Potential Energy

• Equation
• Units

Answer 22

The energy held by an object because of its position relatively close to other objects, stresses within itself, its electrical charge, or other factors.

1. Potential energy (E_p) derived from the Coulomb force (r is the distance between point charges q₁ and q₂). E_p = k q₁q₂/r
2. E_P derived from the universal attraction force ( r is the distance between the COG of masses m₁ and m₂). E_p = G m₁m₂/r
3. E_p derived from the elastic force (i.e. a compressed spring): E_p = kx²/2. (k = spring constant, x = displacement cf).

Question 23

Kinetic Energy

• Units
• Equations

Answer 23

E_k is the energy of motion which can produce work. It is proportional to the mass of the object and its velocity:

E_k = 1/2 mv²

1. The work-energy theorem. A net force is the sum of interior and exterior forces acting upon a system. W (of the resultant forces) = /_\E_k

Question 24

Power

• Units
• Equation

Answer 24

The power P applied during the work W performed by a force F is equal to the work divided by the time necessary to do the work

P = /_\W / /_\t

Power = watt (W) which equals J/s

P = Fv