Kinematics Flashcards
What is uniform acceleration?
An object that accelerates constantly
What does SUVAT stand for? with units
s - displacement (m)
u - initial velocity (ms^-1)
v - final velocity (ms^-1)
a - acceleration (ms^-2)
t - time (s)
What are the 4 formulas you need to know for kinematics?
- v = u + at
- s = ut + 1/2 at^2
- v^2 = u^2 + 2as
- s = (v+u)t / 2
What is the method for the free-falling object practical
- Set up apparatus (make sure your light gates are at equal distances from each other)
- Place your object at the rest position (make sure your object is big enough to be detected by the light gates)
- Drop the object down the tube
- Record the time taken for it to fall down the tube
- Repeat this 5 times and take a mean
- Record the height
- Input the values into the s = ut + 1/2 at^2 formula and find acceleration
How do you minimise errors in the free-falling practical? (name 3 things)
- Take multiple readings - to remove anomalies and take a mean
- Make readings large
- your eye-level when taking readings of time (parallax error)
what are the advantages of using light gates in this practical? (free-falling object) (name 4 things)
- resolution is smaller due to digital readings
- more accurate results
- more readings can be taken - reduce anomalies + mean
- chance of human error reduced
What is the effect of air resistance on the value of g in the free fall experiment?
The higher the air resistance, the lower the value of gravity, as the falling object does not accelerate as much
Why should the graph for the free fall experiment be straight?
It means it is in uniform acceleration
What does the gradient equal in a displacement-time graph?
gradient = velocity
What does the gradient equal in a velocity-time graph?
gradient = acceleration
What does the graph look like for stationary motion in a displacement time graph?
It is a flat, horizontal line
What does the graph look like for constant velocity in a displacement time graph?
It is a straight, diagonal line
What does the graph look like for acceleration in a displacement time graph?
It is an upwards curve
What does the graph look like for constant velocity in a velocity-time graph?
It is a flat, horizontal line
What does the graph look like for uniform acceleration in a velocity-time graph?
It is a straight, diagonal line
What does the graph look like for non-uniform acceleration in a velocity-time graph?
It is an upward curve
What is a Frame of reference?
When you are standing on the ground, that is your frame of reference
What is an inertial frame of reference?
Systems where no forces are acting (i.e. constant velocity)
What is velocity?
Speed in a specific direction
What is relative velocity?
Velocities of the observers relative to the Earth
If two objects are travelling in the same direction at 3m/s, what is their relative velocity?
0m/s
If two objects are travelling in opposite directions, at 3m/s?
6m/s
What is the general method for calculating relative velocity?
same direction = -
opposite direction = +
How do you add vectors (find the resultant velocity)?
Pythagoras Theorem
A motorboat is travelling at 4m/s east and encounters a current travelling 3m/s north. What is the resultant velocity? and angle?
(hint: draw a diagram)
5m/s 37 degrees above east
If the width of the river is 80m wide, how much time does it take for the boat to travel shore to shore?
d/s = t
80/4 = 20 seconds
What distance downstream does the boat reach the opposite shore?
s x t = d
20 x 3 = 60m
Why might a head-on collision usually be most dangerous (car crash)?
When two cars crash head-on, their velocities add up, therefore, they crash with a larger relative velocity. e.g. 30 m/s —> <—30 m/s
= 60 m/s crash = more dangerous
If I throw a paper projectile horizontally, will it reach the ground in more or less time than if I drop it?
It will reach the ground at the same time because they both have the same force of gravity acting on them, therefore they are accelerating at the same magnitude of 9.8m/s
How might a paper plane be different when you throw it versus a paper ball?
The force of lift is against gravity and keeps the plane lifted in the air for longer. This is because the paper aeroplane has a larger surface area, so more air particles hit the wings and lift it up
What force of motion affects the horizontal component of a projectile?
constant velocity
What force of motion affects the vertical component of a projectile?
uniform acceleration
What assumptions can we make when when throwing a paper ball?
That there is no air resistance. Air resistance is negligible
If a hunter and a monkey are at the same height, what will happen if the hunter shoots the bullet at the same time as the monkey drops from the tree? why?
The bullet will hit the monkey. This is because both the bullet and the monkey both have the same force of gravity acting on them at the same magnitude of acceleration
What will happen if the hunter was further away from the monkey?
The bullet will still hit the monkey, just further down in its path
What will happen if the bullet had a greater speed?
The bullet will still it the monkey, just much earlier in its path
What 2 motions do horizontal projectiles consist of?
- A vertical motion
- A horizontal motion
If a question is asking for ‘time’ or ‘height’, what motion do you look at?
Vertical
What is the range?
The horizontal distance
What does the initial velocity equal in vertical motion? and why?
initial velocity = 0m/s
this is because when you drop something vertically, it starts with 0m/s
What equations do you use for vertical motion?
SUVAT
What does v and u equal in horizontal motions?
v = u
What does the acceleration equal in horizontal motion?
TRICK QUESTION!
In a horizontal motion, the projectile does not accelerate, it moves at constant velocity. Therefore, the acceleration = 0
What equation would you use for horizontal motion?
s = d/t
A man standing at the top of a cliff, 150m high, throws a ball horizontally at a speed of 4m/s.
a) Find the time it takes for the ball to reach the ground.
b) Find the horizontal distance the ball travels
a) Vertical motion
s = ut + 1/2at^2
s 150
u 0
v X
a 9.8
t ?
150 = 1/2 (9.8)(t^2)
150 = 4.9t^2
t = 5.53 seconds
b) Horizontal motion
s ?
u 4
v 4
a no acceleration
t 5.53
d = s x t
d = 5.53 x 4
d = 22.13m
An object is thrown horizontally from the roof of a building. What will the displacement graphs look like for the vertical and horizontal motion?
vertical - curved upwards line
horizontal - straight upward line
A ball of paper is thrown horizontally with a speed of 2m/s. How long does it take to reach the bottom of a bin, 4m away?
note: if you are trying to find time and vertical motion does not work, try horizontal motion
t = d/s
t = 4/2
t = 2 seconds
A ball of paper is thrown horizontally with a speed of 2m/s. It lands in a bin 4m away. At what height must that ball have been thrown at?
s ?
u 0
v X
a 9.8
t 2 (from previous question)
s = ut + 1/2at^2
s = 19.6m
State any assumptions made with projectile motion
That air resistance is negligible
A ball is thrown from a height of 1.5m from a car travelling at 10 m/s.
How long does it take for the ball to reach the ground?
‘how long’ - vertical
s 1.5
u 10
v X
a 9.8
t ?
s = ut + 1/2at^2
s = 0.55 seconds
A ball is thrown from a height of 1.5m from a car travelling at 10 m/s.
How far does the ball travel before it reaches the ground?
‘how far’ - horizontal
S x T = D
10 x 0.55 = 5.5 m
An aeroplane drops a package when travelling 13000m above the ground. The package travels a horizontal distance of 12800m. How long does it take for the package to reach the ground?
‘how long’ - vertical, therefore we use the vertical height
s 13000
u 0
v X
a 9.8
t ?
s = ut +1/2at^2
t = 51.5 seconds
An aeroplane drops a package when travelling 13000m above the ground. The package travels a horizontal distance of 12800m. How fast was the plane going?
‘how fast’ - horizontal
S = D/T
S = 12800/51.5
S = 248.5m/s
How do you find the initial velocity of a horizontal and vertical motion of a projectile at an angle?
horizontal - ucostheta
vertical - usintheta
How does a parachute slow you down?
The drag force resists the downward movement of gravity, pushing the parachute back up. As the parachute falls, the drag increases until it just balances out the pull of gravity. At that point, the parachute stops speeding up and begins to fall at a steady speed.
