Motion levels 7-9

Question 1

Explain how to calculate the acceleration on a velocity time graph

Example: what is the acceleration of this graph between 15 and 40 minutes?

Answer 1

Acceleration is found from the gradient of the velocity time graph. A negative gradient means that the object is slowing down, while a positive gradient means that it is speeding up.

Example: the object changes velocity from 60 to -40 in 25 minutes.

This is a change of -100m/s in a time of 1500s

acceleration = change of velocity/time

= -100/1500

= -0.07m/s²

The negative gradient shows that the object is deccelerating

Question 2

Explain how to calculate the total distance travelled by this object

Answer 2

To solve this you can ether:

1. work out the area of one square, count the number of squares and then multiply up
2. Split the graph into sections of shapes where you can work out the area mathematically. Then work out the area under each part and add them together

Question 3

Explain how to find the initial velocity of an object that has accelerated up to a speed of 12m/s, at an acceleration of 5m/s over a distance of 2m

Answer 3

To answer this question you use the equation

v² - u²= 2as

You then treat v²-u² as a single entity (x) and solve for that equation:

x = 2as

=2 x 5 x 2

= 20

Then equate this value to v² - u² to find u²

v² - u² = 20

u² = 12² - 20

u² = 144 - 48

u² = 98

Then use this to find u:

u = √98

= 9.9 m/s