8: Motion

Question 1

What is the difference between a scalar and a vector?

Answer 1

A scalar has no direction - it’s just an amount of something

A vector has a magnitude and a direction

Question 2

How do you find the resultant vector?

Answer 2

Adding two or more vectors together

Question 3

Define speed

Answer 3

How fast something is moving, regardless of direction

Question 4

Define displacement

Answer 4

How far an object’s travelled from its starting point in a given direction

Question 5

Define velocity

Answer 5

The rate of change of an object’s displacement (its speed in a given direction)

Question 6

What is instantaneous speed?

Answer 6

The speed of an object at any given moment in time

Question 7

What is the average speed?

Answer 7

Total distance covered, over the total time elapsed

Question 8

What is another way of saying uniform acceleration?

Answer 8

Constant

Question 9

Define free fall

Answer 9

The motion of an object undergoing an acceleration of ‘g’. Only gravity

Question 10

What is/are the force(s) acting on an object in free fall?

Answer 10

Weight

Question 11

Describe the rate of free fall for different objects

Answer 11

All objects free fall at the same rate

Question 12

What is the main uncertainty in the experiments (light gates and trapdoor) to find the value g?

Answer 12

The height h

Question 13

What is parallax, in the context of uncertainties?

Answer 13

Systematic error due to looking at the ruler at an angle

Question 14

In a graph of displacement against time, how can you tell that something is accelerating?

Answer 14

Graph is curved

Question 15

What does the graph (displacement against time), look like if the object is accelerating at a uniform rate?

Answer 15

Rate of change of the gradient will be constant

Question 16

In a displacement time graph:

If there are two objects, both accelerating, how can you tell which is accelerating more?

Answer 16

Steeper curve

Question 17

In a displacement time graph:

If there are two objects, both accelerating, how can you tell which is accelerating less?

Answer 17

Shallower curve

Question 18

In a displacement time graph:

How can you tell if object is decelerating?

Answer 18

The line has a deceasing gradient - so more like √x graph

Question 19

What does the gradient of a displacement time graph tell you?

Answer 19

The velocity

Question 20

How do you find the instantaneous velocity of an object, using the displacement time graph?

Answer 20

Draw a tangent and calculate the gradient

Question 21

What does the gradient of a velocity time graph show you?

Answer 21

Acceleration

Question 22

Uniform acceleration is always a [ ], on a velocity time graph

Answer 22

Straight line

Question 23

The steeper the gradient, the [ ] the acceleration

Velocity time graph

Answer 23

greater

Question 24

What is the area under a velocity time graph?

Answer 24

Displacement

Question 25

What shows that the acceleration is increasing on a velocity time graph?

Answer 25

Increasing gradient

Question 26

What shows that the acceleration is decreasing on a velocity time graph?

Answer 26

Decreasing gradient

Question 27

What do free-body force diagrams show?

Answer 27

Show a single body on it own

Question 28

Which forces are shown on a free body diagram?

Answer 28

Forces that act on the body, but not the forces it exerts on the rest of the world

Question 29

If a body is in equilibrium, the forces acting on it will be [ ]

Answer 29

Balanced

Question 30

How do you find the resultant force on a body?

Answer 30

Add the vectors (of the forces) together

Question 31

Describe the accuracy of data loggers

Answer 31

They do not have human error and can calculate the velocity and display it in real time – saving time and allowing comparisons between experiments to be easily made

Question 32

Briefly describe how iterative methods can be used for modelling displacement/velocity

Answer 32

Velocity and displacement are calculated over lots of small tiny increments/intervals of time to model their motion over a period of time

Question 33

problem with iterative models, example

Answer 33

graphs don't look realistic
they assume no change occurs within the sampled
time intervals (eg. if the calculation is applied at 5 second intervals, it is assumed that the
motion is constant between 5 and 10 seconds).

Question 34

how to improve iterative models

Answer 34

The accuracy of iterative models can

always be improved by decreasing the time interval.

Question 35

what are vectors

Answer 35

quantities with both magnitude and direction

Question 36

suvat equation not given in booklet regarding 
s
u
v
t

Answer 36

s = (u+v / 2) * t
s - displacement / m
u - initial velocity / m/s
v - final velocity / m/s
t - time / s

Question 37

overall stopping distance of a car

Answer 37

the sum of its thinking distance and braking distance

Question 38

what can affect overall stopping distance of car and how

Answer 38

the speed of the vehicle; the faster it is travelling, the greater distance it will travel in the same time it takes for the driver to react, hence producing a
larger thinking distance. The car will also need to undergo a greater braking force, resulting
in an increased braking distance.

Question 39

advantages of iterative modes

Answer 39

can be used for difficult calculus problems

Question 40

how to calculate new value of v

Answer 40

a = Δv / Δt -> Δv = aΔt

Question 41

how to calculate new value of s

Answer 41

v = Δs / Δt -> Δs = vΔt

Question 42

how to calculate value of acceleration for iteration

Answer 42

a = 9.8 - kv^-²
k = constant

Question 43

how do thinking and braking distance increase with doubling speed

Answer 43

thinking distance doubles

braking distance quadruples because of:

average speed doubling

Δv has doubled from 30 to 60, time taken for deceleration has doubled