Chapter 3 - motion

Question 1

Stopping distance

Answer 1

Thinking distance + braking distance

Question 2

Effect of speed on thinking distance

Answer 2

It goes up in a linear relationship if we assume that reaction time remains the same

Question 3

Effect of speed on braking distance

Answer 3

It goes up in an exponential relationship (faster speed and takes longer)

Question 4

Braking distance

Answer 4

The distance travelled by a vehicle from the moment the brake pedal is pressed until when it stops

Affected by:

• Speed of the vehicle
• Road conditions (wet,icy etc)
• Condition of the vehicle (brakes,tyres etc)

Question 5

Thinking distance

Answer 5

The distance travelled from the moment the driver sees the hazard until the moment they touch the brake

Affected by:

• Speed of the vehicle
• Distractions (mobile phones, radio etc)
• Awareness (tiredness, alcohol, drugs etc)

Question 6

Thinking distance equation

Answer 6

speed x reaction time

Question 7

acceleration with regards to displacement

Answer 7

v^2 - u^2
a = ————-
2s

Question 8

Free fall

Answer 8

An object which is accelerating under gravity with no other forces acting on it

Question 9

Acceleration due to gravity

Answer 9

Denoted by g, given the unit ms-2

Question 10

Projectile motion basics

Answer 10

The horizontal and vertical components of motion are independent from each other

No matter which direction something is released in it will always take the same amount of time to fall if it starts and ends at the same height

Question 11

Projectile motion rules if we assume there is no air resistance

Answer 11

Vertical velocity changes due to the acceleration due to gravity
The vertical displacement and time of flight can be calculated using SUVAT
Horizontal velocity remains constant

Question 12

Projectile motion when fired at an angle

Answer 12

Initial velocity = v
Horizontal comment = v cos(theta)
Vertical component = v sin(theta)

Question 13

Proving that braking distance is directly proportional to speed squared

Answer 13

v^2 = u^2 + 2as
v = 0 so u^2 + 2as = 0
s = -u^2/2a

Question 14

How to go about solving SUVAT questions?

Answer 14

Write down the letters of SUVAT and the information you have for each, use this to choose and potentially rearrange an equation

Question 15

What does each letter in SUVAT mean?

Answer 15

s = displacement
u = initial velocity
v = final velocity
a = acceleration
t = time

Question 16

SUVAT equations

Answer 16

v  = u + at
s = 1/2(v+u)t
v^2 = u^2 + 2as
s = ut + 1/2at^2
s = vt - 1/2at^2

Question 17

How to work out displacement from a v/t graph

Answer 17

Work out the area under the line

If curved count squares, counting all with over half below the curve

Question 18

Curve on a v/t graph

Answer 18

Upward means acceleration or decreasing deceleration

Downwards means deceleration or decreasing acceleration

Question 19

Lines on a v/t graph

Answer 19

Constant acceleration if upwards
No acceleration (constant velocity) if flat
Constant deceleration if downwards

Question 20

What do speed/velocity calculations give you?

Answer 20

The average value

Question 21

Instantaneous speed

Answer 21

The speed of an object at one point, find using a gradient at that point

Question 22

Symbol for speed or velocity

Answer 22

v

Question 23

Symbol for distance

Answer 23

x

Question 24

Distance/time graph

Answer 24

Gradient = speed
Upward curve = accelerating
Flat line = stationary
Downwards gradient = returning to start