2 Mechanics Flashcards

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1
Q

velocity, v [m s-1]

A

rate of change of displacement with time
v = s/t

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2
Q

acceleration, a [m s-2]

A

rate of change of velocity with time
a = ∆v/∆t

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3
Q

(translational) equilibrium

A

resultant force = 0 → acceleration = 0

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4
Q

conserved

A

maintains a constant total value
eg. KE is conserved in elastic collisions; total mechanical energy is conserved when friction is negligible and KE/PE are not changed to other forms (such as sound, internal energy)

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5
Q

conservation of energy

A

energy can not be created or destroyed, it can only change form

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6
Q

Newton’s 1st law

A

a body will remain stationary or at constant velocity unless a net force acts on it

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7
Q

Newton’s 2nd law

A

F = ma

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8
Q

Newton’s 3rd law

A

every applied force has an EQUAL and OPPOSITE reaction force (same size, same type, opposite direction) eg. man on earth ⇔ earth on man)

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9
Q

impulse, Δp [kg m s-1] or [N s]

A

the CHANGE IN MOMENTUM of a body

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10
Q

law of conservation of momentum

A

For an ISOLATED system (no external force);
momentum before = momentum after (collision);
(m₁u₁) + (m₂u₂) = (m₁+m₂)(v)

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11
Q

work, W [J]

A

work done = energy transferred=force × distance moved in the direction of the force
W = ∆E = F * d

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12
Q

kinetic energy, KE [J]

A

energy due to MOTION
KE = ½ mv² = ½ m(v²-u²)

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13
Q

potential energy, PE [J]

A

energy due to RELATIVE POSITION
GPE = mg∆h

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14
Q

elastic collision

A

both MOMENTUM and TOTAL KE are conserved → KE before = KE after

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15
Q

terminal velocity

A

MAX velocity when forces are BALANCED

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16
Q

If v and a are in the same direction, the object…

A

accelerates

17
Q

If v and a are in the opposite direction, the object…

A

decelerates

18
Q

What is the area of a-t graph?

A

∆v

19
Q

For projectile motion, MAXIMUM HEIGHT means?

A

t = t/2
v=0

20
Q

Describe the effects of air resistance on a projectile (height, range, shape)

A
  • Lower max height
  • Shorter range
  • Smaller acceleration downwards

Air resistance increases as velocity increases until reaching terminal velocity where drag=mg!!

21
Q

when forces are balanced, the object is…

A

at rest or moving at constant speed

22
Q

moving at CONSTANT SPEED means…

A

forces are balanced→ net force =0→ acceleration = 0

23
Q

Explain how you make a bicycle go forward in terms of Newton’s 3rd Law:

A

tyres roll and push backward on the ground → ground exerts equal and opposite reaction force, pushing the tyres forward

24
Q

If two objects hang over a pulley or are connected with a rope, it means…

A

Same T (tension)
Same a (acceleration)

25
Q

If two objects travel in opposite direction, they have ____ for velocity/momentum

A

opposite signs!

26
Q

Explain how conservation of momentum applies as a book falls towards the surface of the Earth.

A

Forces on E and B are equal and opposite (3rd Law)

∆P = F∆t → ∆P of E and B are also equal and opposite → P stays as zero

27
Q

Explain how increased DEFORMATION of the golf club can increase the SPEED at which the golf ball leaves the club

A

increase deformation = increased DURATION of contact (∆t)

∆P = F∆t = m(v-u)
∆t increase → v increase

28
Q

Explain why a rocket accelerates forward in terms of momentum and Newton’s Laws

A

CHANGE IN MOMENTUM of the gas gives rise to a FORCE on the rocket that pushes it forward (F=∆P/∆t = ma)

29
Q

What is the properties of an explosion (eg. nuclear fission, bullet leave gun)?

A

momentum = 0
KE increase

30
Q

With reference to forces, explain why a person riding bicycle travels in constant velocity.

A

Vertical : mg=2N
Horizontal: backward force of tyre on ground = forward force of ground on tyre (Newton’s 3rd law)
Resultant force F=0 → a=0 (Newton’s 2nd Law)

31
Q

Explain why we feel ‘weightless’ while riding a rollercoaster.

A

we fall at the same rate as the rollercoaster → no resultant contact force