total distance

Total distance is 0.5*5*30+|0.5*-20*15| = 75+150 = 225m

Total displacement = 0.5*5*30+(0.5*-20*15) = 75-150 = -75m

yes your answer is correct but I don't understand why you take 15 !! why not 20  

in this step ! 

0.5*5*30+|0.5*-20*15|

I don't understand.  I didn't take 15.  It was -20 m/s      

yes yes ... now its very clear .. thank you melody ... 

You are very welcome  

I am going to add this as an interest question so I thought I would comment a little further.

The vertical axis is m/s   the horizontal axis is seconds.

When you multiply these together the seconds cancel out and you are left with metres which is distance.

When you find the area of a rectangle it might be metres * metres so the units will be m^2

When you find the area under these lines the units are  m/s and seconds so the resultant unit is metres.

That is why you can find the distance travelled by finding the area under the curve.

If you have any comments or questions please post here. This is a really interesting and important concept.

Thanks for that explanation, Melody...I don't "do" Physics but I see what you are talking about.....!!!!

Thanks Chris.   

Actually, now that i look at the actual graph it is really weird.

How can you go from +30m/s to -20m/s  in an instant.  Maybe it is in a different universe?   

what I said before still goes though.  

Ninja has asked a question.

"This distance/displacement question does looks interesting. 

I understand the steps to solve and the other numbers, but where do you get 0.5 from?"

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What I needed to find was the area between the curve (line) and the time (horizontal) axis.

The shape of this area is a triangle so I used the formula for the area of a triangle, THAT is where the 0.5 came from.      

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Maybe you could do a one off Ninja and pop this into the great answers to learn thread and pop it in under Physics?   If you don't it doesn't matter.