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Physics H > Our dynamic universe > Flashcards

Our dynamic universe Flashcards

1
Q

sign convention

A

accelerating left -
accelerating right +
accelerating up +
accelerating down -

(like multiplying eg decelerating left= +

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2
Q

What do we use if something is decelerating due to gravity?

A

-9.8ms-2

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3
Q

motion time graphs for constant velocity, uniform acceleration and uniform deceleration
show s,v and a

A

CONSTANT VELOCITY
s/
v—
a__ (@0)

UNIFORM ACCELERATION
s-curve up getting steeper
v/
a—

UNIFORM DECELERATION
s-curve up getting less steep
v\
a— (negative)

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4
Q

What does the gradient of a velocity time graph give?

A

the value of the constant acceleration

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5
Q

What is happening when a velocity time graph crosses the x-axis?

A

a change in direction

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6
Q

draw a bouncing ball graph

A

jotter

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7
Q

For the light gate acceleration experiment, what is needed? (apparatus and measurements)

A

-QED/computer timer
-tow light gates
-trolley with mask
-stop clock

-initial speed
-final speed
-time

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8
Q

component of forces for F, Fvertical and Fhorizontal

A

F is acting at an angle x

horizontal component=Fcosx

vertical component=Fsinx

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9
Q

solving systems of masses problems

A

1-free body diagram (label all forces)
2-find unbalanced for (using total mass)
3-find acceleration (using F=ma)
4-split system into individual bits (label only forces acting on the bit you’re interested in(to find unknown tension or friction))

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10
Q

What is the component of weight parallel to the slope?

A

mgsinx

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11
Q

What is the component of weight perpendicular to the slope?

A

mgcosx

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12
Q

lift problems

direction of unbalanced force, F, for
1-constant speed or stationary
2-accelerating up
3-decelerating up
4-accelerating down
5-decelerating down
6-freefall

A

1-no unbalanced force R=W
2-upwards R-W
3-downwards W-R
4-downwards W-R
5-upwards R-W
6-downwards W only

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13
Q

What is momentum

A

The momentum of an object is defined as its mass multiplied by its velocity

p=mv
kg ms-1

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14
Q

Momentum experiment measurements

A

-velocity of trolley A through light gate 1
-velocity of trollies A and B through light gate 2
-mass of trolley A
-mass of trolley B
-mass of trolley A+B

-calculate the total momentum’s of both trolleys before and after the collision

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15
Q

What is the law of conservation of momentum? +equation

A

‘In the absence of external forces, the total momentum before a collision equals the total momentum after the collision

mAuA + mBuB = mAvA + mBvB

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16
Q

Is sign convention needed for momentum questions and collision questions

A

momentum-YES
collision-NO (as Ek is a scalar quantity)

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17
Q

Is total energy always conserved in any interaction?

A

Yes, but for the questions we must focus on kinetic energy when describing elastic and inelastic collisions

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18
Q

What is an elastic collision?

A

The total kinetic energy of both objects is equal before and after the collision (kinetic energy is conserved)

momentum is also conserved

19
Q

What is an inelastic collision?

A

The total kinetic energy of both objects after the collision is less than it was before the collision (kinetic energy is not conserved)

momentum is conserved

20
Q

What happens to momentum and kinetic energy after an explosion?

A

momentum is conserved

kinetic energy is gained

21
Q

What is the impulse of a force?
+equation

A

The change in momentum of an object

It is equal to the change in momentum of an object involved in the interaction and is also equal to the area under a force-time graph

Impulse=mv-mu
kg ms-1

Impulse=Ft

Ft=nvm-mu (data sheet)

22
Q

What happens if you increase the time of contact in a collision?

A

the average force exerted will decrease (because the area under the graph must stay the same)

23
Q

What are projectiles?

A

Projectiles move with a curved path because they have a combination of both horizontal motion (constant) and vertical motion which act independently (not constant)

24
Q

Do you need sign convention for projectiles?

A

YES

25
Q

What initial vertical velocity will projectiles launched upwards have?

A

non-zero

26
Q

What do projectiles accelerate vertically at?

A

-9.8ms-2

27
Q

What is the equation for vertical and horizontal components of the velocity?

A

vertical v=vsinx

horizontal v=vcosx

v acting at angle to vh can be worked out using pythagoras

28
Q

what is the vertical velocity at the top of the projectile?

A

0ms-1 as there is a change in direction

29
Q

what is the final vertical velocity equal to?

A

the initial vertical velocity but the opposite sign

30
Q

What does G=

A

universal constant of gravitation (6.67x10^-11m^3kg^-1s^-2)

not the same as g

31
Q

What is gravitational field strength g?

A

the amount of force applied to each 1kg of mass (by a gravitational field)

32
Q

What do you need to remember when doing a gravitational force of attraction question with planets?

A

the radius of each planet

33
Q

What does the r= in gravitational force of attraction questions?

A

distance

34
Q

Experiment to measure acceleration due to gravity

A

F=ma
w=mg

electronic timer
height
timing plate
ball
clamp stand

The timer starts when the ball is released and stops when the ball reaches the timing playe

35
Q

What is the gradient of a graph plotted with 2s (y) against t^2 (x)

A

9.8 (gravity)

36
Q

What does it mean if 2 things are in the same reference frame?

A

They are moving at the same velocity (speeding and direction)

37
Q

What does it mean if something is moving relative to you?

A

It is in another reference frame

38
Q

What are einstein’s 2 postulates of special relativity?

A

1-when 2 observers are moving at constant velocities to one another, they will observe the same laws of physics

2-the speed of light (in a vacuum) is the same for all observers in all reference frames

39
Q

What is time dilation?

A

a difference (increase) in a time interval as measured by a ‘stationary’ observer and a moving observer

40
Q

what is t and t prime? and v

A

t-time measured by an observer in the same reference frame as the event
-proper time

t prime-time measured by an observer in a different reference frame to the event
-dilated time

v-speed of relative motion between 2 reference frames

41
Q

What is length contraction?

A

A difference (decrease) in length as measured by a ‘stationary’ observer and a moving observer

42
Q

what is l, l primer and v?

A

l-proper length

l prime-contracted length

v-speed of relative motion between 2 reference frames

43
Q

what is c?

A

speed of light

Physics H (5 decks)

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