1
Q
State the word equation for average speed
A
- average speed = distance travelled / time taken
2
Q
A
3
Q
A
4
Q
A
5
Q
A
6
Q
A
7
Q
A
8
Q
A
9
Q
A
10
Q
State the symbol equation for average speed
A
- v = delta x / delta t
11
Q
A
- Graphs of distance against time are used to represent the motto of objects
12
Q
A
13
Q
A
- Distance is plotted on the y-axis
- Time is plotted on the x-axis
14
Q
A
- In a d-t graph, a stationary object is represented by a horizontal straight line
- An object moving at a constant speed is represented by a straight, sloping line
- The gradient of that line is equal to the the speed of the object
15
Q
Define instantaneous speed
A
- The speed of the car over a very short interval of time
16
Q
How is the instantaneous speed of a particular time found?
A
- By drawing the tangent to a d-t graph then determining the gradient of the tangent
- The greater the gradient, the greater the instantaneous speed
17
Q
What is the direction of instantaneous velocity?
A
- Tangential to the path
18
Q
Describe displacement
A
- vector quantity with magnifier and direction
19
Q
Describe distance
A
- Scalar quantity,
20
Q
How is speed calculated
A
- Speed is scalar quantity calculated from distance
21
Q
A
- Velocity is a vector quantity calcuetd from displacvtemtn
22
Q
State the word equation for average velocity
A
- average velocity = change in displacement / time taken
23
Q
State the symbol equation for average velocity
A
v = delta s / delta t
24
Q
A
- graphs of displacement against time are used to represent the motion of objects
25
* Displacement is plotted on the y axis
* Time is plotted on the x axis
26
* If a car is travelling at a constant velocity, the line is sloping upwards
* For the displacement of the car remains constant, it is horizontal, therefore the car must be stationary
If there is a negative slow, the displacement of the car is getting smaller with time, car must be retiring to a constantly velocity
27
* You can determine the velocity of an object from the gradient
* If not a straight line draw a tangent to determine instant velocity
28
Define acceleration
* Rate of change of velocity
29
State the word equation for acceleration
* acceleration = change in velocity / change in time
30
State the symbol equation for acceleration
* a = delta v / delta t
31
State the unit of acceleration
ms-2
32
What is a negative acceleration often called?
* deceleration
33
Is acceleration a scalar or vector quantity?
* Determined from velocity, therefore vector
* Has magnitude and direction
34
* in a velocity time graph - y axis represents velocity
35
* acceleration = gradient of velocity time graph
36
* A straight line of constant positive gradient = constant acceleration
* straight line of zero gradient= constant velocity or zero acceleration
* a straight line of constant negative gradient : constant deceleration
* curve with a changing gradient : accerleration is changing
37
* Tachographs record the speed and distance travelled by a vehicle
38
* change in displacement to equal to area under the graph
39
* when acceleration is constant, displacement is easy to calculate because the areas can be broken down into rectangles and right angle triangles
40
* for non linear velocity time graphs you cam determine the area under the graph by counting squares
41
* need four equations to calculate quantities involving motion in a straight line at a constant acceleration (SUVAT)
42
velocity time graph equations from the graph
Gradient = (v-u)/t
Area = 1/2 x (v-u) x t - rectangular area
area = u x t - triangular area
43
state
v = u + at
44
equation without v
substitute v-u = at into area of a triangle expression
s = ut +1/2at^2
45
equation without a
if u treat area under graph as area of trapezium and use u and v as parallel side of trapezium and t as perpendicular separation
s = 1/2 (u+v)t
46
equation without t
v2 = u2 + 2as
47
how do u get v2 = u2 +2as
t = v-u / a
s = 1/2 (u+v) x (v-u) /a
48
Define stopping distance
* The total distance travelled from when the driver first sees a reason to stop, to when the vehicle stops
49
State the two components of stopping distances
* Thinking distance
* Braking distance
50
Define thinking distance
* The distance travelled between the moment when you first see a reason to stop, the moment when you use the brake
51
Define braking distance
* The distance travelled from the time the brake is applied until the vehicle stops
52
State some factors that influence stopping distance
* Speed of vehicle
* The condition of brakes, tyres and roads
* Weather conditions
* Alertness of drivers
53
State the word equation for thinking distance
* thinking distance = speed x reaction time
54
* The greater the speed or reaction time, the further a vehicle will travel before its drivers applies the brakes
55
* Assuming a constant the reaction time of 0.67s the thinking distance will be about 21m
uk national speed limit of 70mph
56
in the uk Highway Code the braking distance at 30mph is shown as 14m
if you assume constant deceleration from 14.3 to 0 ms-1 you can use one of the equations of motion to determine the magnitude of the deceleration
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3.7
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3.8
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Physics M3 (forces & motion)
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