P 2. Kinematics Flashcards
Is displacement vector or scalar?
and why?
- Vector
- Magnitude & direction
Is distance vector or scalar?
and why?
- Scalar
- No need to state its direction
Define speed?
The distance travelled in unit time
Define velocity?
The change of displacement per unit time
How to find average speed/velocity?
S = D/T
And that’s why it’s m/s O_o
Define acceleration?
The change of velocity per unit time
How to find average acceleration?
m/s² = m/s/s
that’s why it’s m/s² O_o
Acceleration formula in word form
Acceleration = Change in velocity/time taken
What are the 6 features in a displacement-time graph?
(and their definitions)
- Constant speed = Straight hill
- Stationary = Straight
- Negative direction = Going down
- Positive direction = Going up
- Acceleration = arc upwards
- Deceleration = arc downwards
What does the gradient in a displacement-time graph give u?
Velocity
(average speed)
What happens if u gain the negative gradient?
Negative velocity
(opposite direction)
What are the 5 features in a velocity-time graph?
(and their definitions)
- Constant acceleration = Straight hill up
- Constant speed = Straight
- Deceleration = Straight hill down
- No arcs
- There’s still positive/negative directions
What does the gradient give u in a velocity-time graph?
Acceleration
(m/s2)
What does the area under line give u in a velocity-time graph?
Displacement
What about area under their negative lines?
Negative displacement
(therefore ya minus when adding altogether)
Where do u find suvat equations?
…. in the damn data booklet.
Define s
(suvat)
Displacement
Define u
(suvat)
Initial velocity
Define v
(suvat)
Final velocity
Define a
(suvat)
Constant acceleration
Define t
(suvat)
Time
How to find initial velocity (u) in v-t graph?
The starting point of the “rise”
(Straight hill)
How to find the final velocity (v) in v-t graph?
The ending point of the “rise”
(Straight hill)
How do u derive V = u + at?
(4 steps)
- v-t graph (velocity time graph)
- Gradient = rise/run
- a = (v-u)/t
- Re-arrange to turn into the formula
v = u + at
How do u derive S = ½ (u+v) t?
(5 steps)
- v-t graph (velocity time graph)
- Displacement = average velocity x time
- Average velocity = (u+v)/2
- s = ((u+v)/2) x t
- Re-arrange to turn into the formula
s = ½ (u+v) x t
How do u derive S = ut + ½at2?
(5 steps)
- Combine:
- S = ½(u+v) x t
- V = u + at - S = ½ (u + {u + at}) x t
- Do everything that it takes to get to the “formula”
- S = 1/2 (u + at) x t
S = ut + ½ at2
How do u derive v2 = u2 + 2as?
(6 steps)
- Use both equations:
- v = u + at
- s = ½ (u+v) x t - Find t of v = u + at
- Sub that equation into second equation
- s = ½ (u+v) x (v-u)/a
- Do everything it takes to get to the “formula”
- s = {(u+v) x (v-u)}/2a
v2 = u2 + 2as
We have a problem, projectile motion. I’d wanna ask for help for this one but ahhh can I at least write summin brief notes?
- Say no air resistance or summin
- Sometimes asked to find horizontal & vertical components (z sin/cos theta)
- Use suvat for height or time of flight
- Range = total horizontal distance
use d = st - Down arc = parabowler
- for acceleration (9.81), going up is negative, going down is positive
Define projectile?
(3 things)
- Any body that is given an initial velocity
- and then follows a path determined by
- the effect of gravity on that object
Define trajectory?
Path followed by a projectile
What are the 2 motions consisting within projectile motion?
- Horizontal motion
- Vertical motion
For the vertical motion y, what is it subject to when going up/down?
How come?
(1 each)
- Deceleration on the way up
- Acceleration on the way down
- Due to gravity
For the horizontal motion x, why does it remain constant?
(2 points)
- Gravity isn’t affected by it
- Which acts only in vertical plane
Tell me about horizontal motion in projectile motion
(Super optional)
- Not affected by gravity
- Remains constant
1. Initial velocity = ucosθ
2. Acceleration = 0
3. Displacement at time t - Use S = ut + 1/2 at2
- We know a = 0
- And to find horizontal displacement = uxt
- ∴ x = (ucosθ)t
4. Final velocity = same as initial velocity - Using v = u + at
- a = 0
- vx = ux = ucosθ
dude just use ucosθ for horizontal component
Tell me about vertical motion in projectile motion
(Super optional)
- Subject to deceleration going up
-
Acceleration going down due to gravity
1. Initial velocity = usinθ
2. Acceleration = -g (initially & -9.81)
3. Displacement at time t - Use S = ut + 1/2 at2
- We know a = -g
- Vertical displacement would be y = uyt - 1/2 gt2
- ∴ y = (usinθ)t - 1/2 gt2
4. Final velocity = initial minus gt - Using v = u + at
- a = -g
- vy = ux
dude just use usinθ for vertical component
What are the 3 types of trajectories for projectile motion questions?
- Normal Projectile Motion
- Trajectory from a cliff
- “Elevated” projectile motion
What isn’t there for a typical projectile motion question?
Air resistance
A word for the shape of path created from a trajectory from a cliff?
Parabola
A “useful” tip for projectile motion questions?
Set out suvat symbols
For a projectile motion, what are the 2 things u must calculate?
(Connection to basic physics)
- Horizontal components
- Vertical components
What is the vertical component equivalent to?
(suvat)
Initial velocity
(u)
What’s the final velocity always at for projectile motion?
… 0
How do u calculate the maximum height reached?
(5 steps)
(Normal Projectile motion)
- Gain suvat from vertical motion part
- Gain u, v & a
- S = ?
- Use V2 = u2 + 2as
- Re-arrange for s
How do u calculate time of flight?
(7 steps)
(Normal Projectile motion)
- Gain suvat from vertical motion part
- Gain u, v & a
- T = ?
- Use V = u + at
- Re-arrange for T
- Always x2 the answer
- As it’s only for the first half of the flight
How do u calculate range?
(4 steps)
(Normal Projectile motion)
- Gain “s”, u & t of horizontal motion part
- S = ?
- Use s = d/t
- Re-arrange for d
How do u calculate time taken until it hits?
(5 steps)
(Trajectory from a cliff)
- Gain suvat from vertical motion part
- Gain s, u, & a
- T = ?
- Use S = ut + ½at2
- Re-arrange for T
How do u calculate the range?
(4 steps… hollon)
(Trajectory from a cliff)
- Gain “s”, u & t of horizontal motion part
- S = ?
- Use s = d/t
- Re-arrange for d
How do u calculate magnitude and direction of resultant velocity?
(7 steps)
(Trajectory from a cliff)
- Gain suvat from vertical motion part
- Gain s, u, a & t
- The shape is like an upside-down right-angled triangle
- Use v = u + at
- Final velocity = the “opposite”
- Pythagoras theorem for resultant velocity
- Trigonometry for direction of resultant velocity
How to answer projectile motion of an elevated trajectory?
(check-uppp)
(still imp too)
3 (Elevated trajectory):
1. Basketball, fadeaway shot, how long it takes for ball to hit ground?
- So this is just purely vertical motion part
- Find vertical component
- Afterwards, hope that it states how high it was released
- Then apparently that height has gotta be negative (could be similar to how going up must be -g)
- Use equation S = ut + 1/2 at2
- And then, u actually just re-arrange to make it into ax2 + bx + c
- Gain values of t by factorising (or use calculator B|)
- Whatever answer u get, obviously it won’t be the negative
(Don’t get confused, keep trying to figure it out, took me a while from the exemplar question)
Albert Einstein said that u learn from starting from the first principles
Revamped successfully?
Unsure about elevated trajectory
However, past papers are a must
Correct
