P2 – Forces and Motion Lesson 3: D-T and V-T Graphs.

Q1. A child goes out to visit a friend. The graph shows the child’s journey.

(a) Calculate the child’s average speed for the whole journey.[Show your working and give the units in your answer.] (3)

(b) How many times faster is the child travelling in part A of the graph than in part C? (2) (Total 5 marks)

a. 140/70 = 2m/sb. 100/20 = 5m/s

40/20 = 2m/s

5/2 = 2.5 times

A

B

C

Distance-Time Graphs:

• The gradient = speed• Flat section are where it’s stopped• The steeper the slope, the faster it is going• Curves represent acceleration

Keywords: Distance-Time, Velocity-Time, Gradient, Keywords: Distance-Time, Velocity-Time, Gradient,

Calculating Speed

You can use a distance-time graph to calculate the speed. All you need to do is work out the gradient.

Gradient = Vertical Horizontal


Time (hours)

Dis

tance

(m

iles)

0 1 2 3 4 5

075

150

x

e.g. 150

5 = 30 mph

(Remember to use the units on the axis)

Q2. The graph shows the speed of a runner during an indoor 60 metres race.

(a) Calculate the acceleration of the runner during the first four seconds. (3)

(b) How far does the runner travel during the first four seconds?(Show your working.) (3)

(c) At the finish, a thick wall of rubber foam slows the runner down at a rate of 25 m/s2.

Velocity-time Graphs:

• The gradient = acceleration • Flat section are travelling at a steady speed• The steeper the slope, the greater the acceleration. • Uphill sections are acceleration. • Downhill section are deceleration• The area under any section is the distance travelled in that time interval. • A curve means a changing acceleration.


How to calculate speed:

How to calculate velocity:

How to calculate acceleration:

Speed and Acceleration What I need to know.

Definitions of key words:

Speed:

Velocity:

Acceleration:

Units Metres Kilometres

Distance Metres (m)

Time Hours (h)

Speed and Velocity

Metres per second (m/s)

Acceleration

Distance-Time graphs:

You can calculate the velocity using a d-t graph by:

Speed-Time graphs:

You can calculate acceleration by:

You can calculate the distance travelled by:

Velocity/TimeDistance/Time

Stopped

Constant Velocity

Constant Acceleration

D

t

D

t

D

t

V

t

V

t

V

t

How to calculate speed:

Speed = distance time

How to calculate velocity:

Velocity = distance time

How to calculate acceleration:

Acceleration = Change in Velocity

time

Δv = change in velocity (e.g. if a car accelerates from 30m/s to 70m/s, its change in velocity is 40m/s.

Speed and Acceleration What I need to know.

Definitions of key words:

Speed: The time is takes to travel a set distance. Velocity:

Acceleration:

Units Metres Kilometres

Distance Metres (m)Time Hours (h)

Speed and Velocity

Metres per second (m/s)

Acceleration

ds t

Δv a td

v t

Same as speed but tells you what direction the motion is in.

The time it takes for change speed.

Seconds (s)

m/s2

Kilometres (km)

Kilometres per hour (km/h)

km/h2

Distance-Time graphs:

You can calculate the velocity using a d-t graph by:Working out the gradient of the graph, i.e. distance/time.

Gradient = Vertical Horizontal

Speed-Time graphs:

You can calculate acceleration by:

Working out the gradient of the graph, i.e. speed/time.

You can calculate the distance travelled by:

Working out the area under the graph.

Velocity/TimeDistance/Time

Stopped

Constant Velocity

Constant Acceleration

D

t

D

t

D

t

V

t

V

t

V

t

Are you now able to….

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P2 – Forces and Motion Lesson 3: D-T and V-T Graphs.

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