Module 3 - Section 1 - Velocity-time Graph

Question 1

What does the gradient of a velocity-time graph tell you ?

Answer 1

Acceleration

Question 2

How do you find the gradient ?

Answer 2

Y/x

Question 3

How does acceleration look like in a velocity-time graph ?

Answer 3

Uniform ( constant ) velocity is always a straight line - this is only in velocity time graphs though - remember that in displacement time graphs acceleration is a curved line

Question 4

In a velocity time graph, the steeper the line the …

Answer 4

The steeper the gradient, the greater the acceleration

Question 5

What’s the equation for a straight line ?

Answer 5

Y = mx + c

Question 6

How can you rearrange the acceleration equation to get the equation for a straight line ?

And what does this show ?

Answer 6

V = u + at

So on a vt graph - a = gradient, u = y intercept

Question 7

When will there be a straight line for a vt graph ?

Answer 7

Only for UNIFORM velocity

Question 8

A lion strolls along at 1.5ms-1 for 4 s and then it accelerates uniformly at a rate of 2.5ms-2 for 4s

Plot this information on a vt graph

Answer 8

First draw a table of results:
For the first 4secs the velocity was 1.5ms-1, then it increases by 2.5ms-1 every second
So draw a table ( time and velocity ) - put from 0-4 secs there was 1.5 velocity and then from 4-8 the velocity increased 2.5 per sec so for e.g. for the 5th sec the velocity would be 4.0ms*-1 as 2.5 + 1.5

Then you just take the points and plot them on a graph

Question 9

How do you find displacement in a vt graph ?

Answer 9

Displacement on a vt graph is - the area under the vt graph

Any negative parts on a graph count as negative areas as they show the object moving back to its starting point

Question 10

What does a curve mean on a vt graph ?

Answer 10

Non-uniform acceleration is a curve on a vt graph

IF the acceleration is changing on a vt graph then the gradient will also be changing - so you wont get a straight line

Question 11

How does increasing acceleration look on a vt graph ?

Answer 11

It is shown by a curved line upwards

Question 12

How does decreasing acceleration look like on a vt graph ?

Answer 12

Decreasing acceleration looks like a curved line downwards

Question 13

How do you find the displacement from a curved vt graph ?

Answer 13

You have to estimate the areas - you have to split the curve into trapeziums - calculate the areas of the trapeziums and then add them up to find the displacement

Area of a trapezium - 1/2(a+b)h

Question 14

Whats the area under a speed time graph ?

Answer 14

It’s the total distance travelled

Question 15

How does constant velocity look like on a velocity time graph

Answer 15

Horizontal line