Basic Physics, Kinematics, Dynamics, Energy Concepts

Question 1

[def] Quantity

Answer 1

In SI: a number x a unit

Question 2

[def] Scalar

Answer 2

Quantity with magnitude only

Question 3

[def] Vector

Answer 3

Quantity with magnitude and direction

Question 4

[def] Resolving a vector into components in particular directions

Answer 4

find vectors (components) in these directions, which vectorially add to make the original vector.
Components are equivalent to original vector

Question 5

[def] Density of a material (ρ)

Answer 5

Density = Mass/Volume
UNIT: kg m−3 or g cm-3
In which mass and volume apply to any sample of the material.

Question 6

[def] Moment of a force

Answer 6

Moment of a force about a point is the force x the perpendicular distance from the point to the pivot
moment = F x d
UNIT: N m [unit is NOT J]

Question 7

[def] Principle of moments

Answer 7

For a system to be in equilibrium, sum of total anticlockwise moments about a point = sum of total clockwise moments about the same point

Question 8

[def] Center of gravity

Answer 8

the single point within a body at which the entire WEIGHT of the body may be considered to act.

Question 9

Random errors

Answer 9

Reduced by repeat readings because they are out of your control

Question 10

Systematic errors

Answer 10

reduced by calibrating the equipment because they are from the measuring equipment (or operator)

Question 11

How to lay out uncertainty

Answer 11

quantity x ± u (then units here)

Question 12

Uncertainty: how much?

Answer 12

Instrument resolution (when one reading)
or
Half the range (when spread of readings)
LARGEST ONE

Question 13

How to reduce uncertainty (x2)

Answer 13

Larger quantity (or divide down)
More precise instrument

Question 14

percentage uncertainty calculation

Answer 14

(estimated uncertainty) / (mean value) X 100 %

Question 15

uncertainty: multiply or divide quantity

Answer 15

add %u

Question 16

uncertainty: multiplied by constant

Answer 16

SAME, UNCHANGED %u

Question 17

uncertainty: raise quantity to power

Answer 17

%u multiplied by same power

Question 18

uncertainty: add or subtract quantity

Answer 18

Add absolute u

Question 19

SI units

Answer 19

kg, m, s, A, mol, K

Question 20

two things to for a system to be in equilibrium

Answer 20

no net moment

no resultant force

Question 21

[def] Displacement

Answer 21

Displacement of point B from point A is the shortest distance from A to B, together with the direction
UNIT: m

Question 22

[def] mean speed

Answer 22

mean speed = (total distance traveled) / (total time taken)
= (delta x) / (delta t)
UNIT: m s-1

Question 23

[def] Instantaneous speed

Answer 23

Rate of chance of distance

UNIT: m s-1

Question 24

[def] mean velocity

Answer 24

mean velocity = (total displacement) / (total time taken)

UNIT: m s-1

Question 25

[def] instantaneous velocity

Answer 25

rate of change of displacement | UNIT: m s-1

Question 26

[def] mean acceleration

Answer 26

mean acceleration = (change in velocity) / (time taken) = (delta v)/ (delta t) UNIT: m s-2

Question 27

[def] instantaneous acceleration

Answer 27

Rate of change of velocity | UNIT m s-2

Question 28

[def] terminal velocity

Answer 28

the terminal velocity is the CONSTANT, MAXIMUM velocity of an object when resistive forces on it are equal and opposite to the 'accelerating' force (ie the pull of gravity)

Question 29

[def] Force, F

Answer 29

A force on a body is a push or a bull acting on the body from some external body UNIT: N

Question 30

Newton's First Law

Answer 30

If an object experiences no resultant force, then its velocity is constant

Question 31

Newton's Third Law

Answer 31

If body A exerts a force on body B, then body B will exert a force on body A that is EQUAL IN MAGNITUDE and OPPOSITE IN DIRECTION N3L pairs = same types of force (gravitational, contact, frictional, magnetic)

Question 32

Newtons's second Law (more 'complex' definition)

Answer 32

The rate of change of momenta of an object is proportional to the resultant force acting on it, and takes place in the direction of that force.

Question 33

Newton's second law ('easier' definition)

Answer 33

(sum of F) = m a Mass of a body x its acceleration is equal to the vector sum of the forces acting on the body This vector sum is called the resultant force

Question 34

s-t graph: Grad? Area?

Answer 34

grad = acceleration area under= distance

Question 35

v-t graph: | Grad?

Answer 35

+ve grad = forwards motion | -ve grad = backwards motion

Question 36

d-t graph: Grad? Line shape?

Answer 36

grad = velocity curved line = accelerating

Question 37

SUVAT

Answer 37

``` v = u +at s= vt - ½a(t^2) s= ut + ½a(t^2) s= ½(v+u)t (v^2)= (u^2) +2as ```

Question 38

Projectile motion: how?

Answer 38

Split into horizontal and vertical components Time will be same Horizontal = s=vt Vertical= SUVAT

Question 39

Projectile motion: Horizontal and vertical - why?

Answer 39

SUVAT vertical because constant acceleration due to gravity s=vt horizontal because we can ignore air resistance PERPENDICULAR COMPONENTS ARE INDEPENDENT OF EACH OTHER

Question 40

[def] Momentum

Answer 40

The momentum of an object is its mass multiplied by its velocity (p = m v). Momentum is a vector. UNIT: kg m s-1 or N s

Question 41

[def] Principle of conservation of momentum

Answer 41

The vector sum of the momenta of bodies in a system stays constant (even if forces act BETWEEN the bodies) Provided there is NO EXTERNAL resultant force.

Question 42

[def] Elastic collision

Answer 42

Collision when there is NO CHANGE in total KE

Question 43

[def] Inelastic collision

Answer 43

Collision when KE is LOST

Question 44

Momentum --> Impulse

Answer 44

N2L: F= ma ----> v/t = a F=(delta m v)/t (force = rate of change of momenta) (delta m v) = F (delta t) Change in momentum = impulse N1L: momentum is constant if there is no external force (F=0 so F t =0) change in momentum=0

Question 45

[def] Principle of conservation of energy

Answer 45

"Energy cannot be created or destroyed, only transferred from one form to another" Energy is a Scalar.

Question 46

[def] Work, W

Answer 46

Work done by a force is the product of the magnitude of the force and the distance moved in the direction of the force. W=F x cos(theta) UNIT: J

Question 47

[def] Potential Energy Ep: Definition and equation

Answer 47

Energy possessed by an object by virtue of its position Ep = mgh UNIT: J

Question 48

[def] Kinetic energy, Ek: Definition and equation

Answer 48

Energy possessed by an object by virtue of its motion Ek= ½m(v^2) UNIT: J

Question 49

[def] Elastic Potential Energy: Definition and equation

Answer 49

Energy possessed by an object when it has been deformed due to forces acting on it Eelastic = ½Fx = ½ k(x^2) k = spring constant, x = stretch or extension UNIT: J

Question 50

[def] Energy

Answer 50

The energy of a body or system is the amound of qork it can do UNIT: J

Question 51

[def] Power, P

Answer 51

Power is the work done per second, or energy transferred per second or rate of work or rate of energy transfer UNIT: W = J s-1

Question 52

Work done equivalent to

Answer 52

Change in KE

Question 53

Stability: more stable (x2)

Answer 53

Lower center of gravity | Wider base

Question 54

Stability: equation

Answer 54

tan(theta) = w/h

Question 55

Stability: when topple?

Answer 55

Object will topple when the center of gravity passes over the corner

Question 56

Friction and drag re efficiency

Answer 56

Friction and drag --> energy transferred from system --> system's efficiency decreases