Module 3 - Section 1 - Displacement- Time Graphs

Question 1

How will the displacement-time graph look like if the object is accelerating ?

And whats happens if the object is accelerating at a uniform rate ?

Answer 1

The graph of displacement against time for an accelerating object will always produce a curve

If the object is accelerating at a constant rate then the rate of change of the gradient will be constant

Question 2

How do you answer a question like this ?

Plot a displacement time graph for a lion who accelerates constantly from rest at 2ms*-2 for 5 seconds

Answer 2

Firstly make a table of results - you have the time so going down put down the time going from 0 to 5 then make another column for displacement - we then have to figure out displacement

You want to find s ( displacement ) and we know that a=2ms-2 and u=0ms-1 because it says that the lion accelerated from rest

You then use the equation of s=ut+1/2at2
When you substitute u in then the equation becomes s=1/2at2 as u=0

So then you substitute a=2 in then you get s=1/2x2t*2

Which then becomes s=t*2 as 1/2x2= 1

So then this means that s=t*2 so for every second the displacement is squared

So then you plot all you displacement points in the table and then draw a displacement time graph

Question 3

How does a displacement time graph look like there is a deceleration ?

Answer 3

The curved line has a decreasing gradient and curves the other way

Question 4

What happens to the graph if there is a bigger acceleration ?

Answer 4

The graph gets steeper

Question 5

What happens to the graph if there is a smaller acceleration ?

Answer 5

There is a less steep graph

Question 6

What does the gradient of a displacement time graph show you ?

Answer 6

It tells you the velocity

Question 7

In a displacement time graph what type of line will occur if the velocity is constant and therefore there is no acceleration ?

Answer 7

There will just be a straight line

Question 8

When there is a straight line on the displacement time graph whats the velocity defined as ?

Answer 8

velocity = change in displacement / change in time

Or change in y / change in x

Question 9

What does it means if the gradient isn’t constant on a displacement time graph ?

Answer 9

If the gradient isn’t constant then it means that the object is accelerating

Question 10

How do you found the gradient if the graph is curved - the object is accelerating ?

Answer 10

You have to draw a tangent and then just do change in your / change in x

So to find the instantaneous velocity on a curved graph you have to draw a tangent

Question 11

How do you find the average velocity over a period of time in a displacement time graph ?

Answer 11

Just divide the final change in displacement / by the final change in time

• It doesn’t matter if the graph is curved or not