Forces 4 - speed/velocity/acceleration/displacement

Question 1

What does distance tell us, what doesn’t it tell us

Answer 1

Distance is how far an object has moved.
Distance does not involve direction (doesn’t say anything about the direction the car moved in only the distance it travelled

Question 2

Explain why distance is a scalar quantitiy

Answer 2

Distance has magnitude but no direction therefore distance is a scalar quantity

Question 3

Define displacement

Answer 3

Displacement includes both the distance an object moves,
measured in a straight line from the start point to the finish point
and the direction of that straight line

Question 4

Explain why displacement is a vector quantity

Answer 4

Displacement includes both magnitude and direction THEREFORE displacement is a vector quantity

Question 5

Give an example of a displacement measurement

Answer 5

380m EAST

Question 6

Define speed

Answer 6

The distance an object has travelled in a given time

Question 7

Equation that links speed, distance and time

Answer 7

Speed = Distance/Time

speed - m/s or km/h
distance - metres or km
time - s or hours

Question 8

Explain why speed is a scalar quantity

Answer 8

Speed has magnitude but no direction therefore speed is a scalar quantity

Question 9

State the typical speeds of:
walking
running
cycling
car
train
plane
speed of sound in air

Answer 9

Typical values may be taken as:
walking ̴ 1.5 m/s
running ̴ 3 m/s
cycling ̴ 6 m/s
car - approx. 13m/s
train - approx. 50m/s
plane - approx. 250m/s
speed of sound in air = 330m/s
the speed of sound can vary - (sound travels faster on warmer days than cooler ones)

Question 10

State the factors which can affect the speed at which a person can walk, run or cycle

Answer 10

The speed at which a person can walk, run or cycle depends on
many factors including:

age, terrain (people move more rapidly on flat ground rather than moving uphill) , fitness and distance travelled

Question 11

What types of speed varies

Answer 11

It is not only moving objects that have varying speed. The speed of
sound and the speed of the wind also vary

Question 12

Define velocity

Answer 12

The velocity of an object is its speed in a given direction

Question 13

State what we are saying speed or velocity
20m/s
20m/s south

Answer 13

20 m/s - stating speed
20m/s south - stating velocity

Question 14

Explain why velocity is a vector quantity

Answer 14

Velocity includes both magnitude and direction, therefore velocity is a vector quanity

Question 15

Equation for velocity

Answer 15

Same for speed
v = s/t

v - velocity
s - distance
t -time

Question 16

A person walks in a straight line from point A to point B covering a distance of 50m
This takes 40s
Calculate the person’s velocity

Answer 16

v = s/t
v=50/40 = 1.25m/s south (the person is south)

Question 17

Explain why the velocity of the car is constantly changing even though a car is travelling at a constant speed in a circle

Answer 17

Even though the car is moving with a constant speed, its direction is constantly changing, therefore its velocity is constantly changing

(if an object moves at a constant speed in a circle then its velocity is constantly changing even though its speed is constant)

Question 18

How can the distance be represented if an object moves along a straight line

Answer 18

If an object moves along a straight line, the distance travelled can
be represented by a distance–time graph.

Question 19

How can be speed of an object be calculated using a distance-time graph

Answer 19

The speed of an object can be calculated from the gradient of its
distance–time graph

Question 20

How can the speed at any particular time be determined for an accelerating object

Answer 20

If an object is accelerating, its speed at any particular time
can be determined by drawing a tangent and measuring the
gradient of the distance–time graph at that time.

Question 21

A person walked 100m in a straight line in 100 s
Then stopped for 40 seconds and then walked another 70 m in 50 seconds

Question 22

What does an upward sloping curve tell us in a distance-time graph

Answer 22

This tells us that the object is constantly increasing in speed (accelerating)

Question 23

How to know the speed at 100s

Answer 23

Place a dot on the line - 100 s
draw a tangent to the line
work out gradient of the line

1.75 m/s

Question 24

What does these lines show:
straight line
flat line
steeper straight line
line going downwards
curve - upward/levelling off

Answer 24

straight line - object travelling at a constant speed
flat - object is stationary
steepening curve - This tells us that the object is constantly increasing in speed (accelerating)
curve levelling off - object is constantly decreasing in speed (decelerating)
line going backwards - the person is going back to their start point, faster at a constant speed

Question 25

Explain why acceleration is a vector quantity

Answer 25

Velocity is a vector quantity as it has both magnitude and direction
The acceleration of an object is the change in its velocity over a given time
therefore acceleration is a vector quantity

Question 26

Define acceleration

Answer 26

The acceleration of an object is the change in its velocity over a given time
therefore acceleration is a vector quantity

Question 27

state the equation that links acceleration, change in velocity, time

Answer 27

a = ∆ v/t
acceleration = change in velocity/time

a = v - u /t

a = m/s^2
v & u = m/s
time in seconds

Question 28

A car accelerated at 1m/s^2 for 20s
what does this mean

Answer 28

The car increased its velocity by 1m/s every second over a 20 second period

Question 29

What does the gradient of a velocity-time graph tell us

Answer 29

The gradient of a velocity-time graph represents the acceleration

Question 30

What does a flat line in a velocity-time graph represent
when gradient = 0

Answer 30

A flat line/horizontal line shows us that the object is travelling at a constant velocity

Question 31

What does an upward and downward sloping/negative acceleration line represent in a velocity-time graph

Answer 31

An upward sloping line shows that the object is accelerating
A downward sloping line shows that the object is decelerating

Question 32

What does a curved line indicate in a velocity-time graph

Answer 32

A curved gradient indicates that the object is either accelerating or decelerating at a non-uniform rate

Question 33

How to calculate the distance travelled in a velocity-time graph

Answer 33

The total area under the graph tells us the distance travelled in a specific direction (displacement)

distance travelled = area under the graph

or
distance travelled - area under graph (calculated by counting squares)

e.g. 20 squares
each square has an area of 250
20 x 250 = total displacement of 5000 m

Question 34

equation that links velocity, displacement and time

Answer 34

v = s/t

velocity = distance travelled in a given direction / time taken

velocity = displacement / time taken

velocity, v in m/s
displacement, s in s
time in s