# What is the answer for question 1. a) http://postimg.org/image/f1kxxqprl/

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### 2 Answers

Speed = Distance / Time

In other words, speed is the slope of your distance graph. So the question is just asking: "What is the slope of the graph at each moment in time?"

So for example:

at time 0, the distance is 10

at time 15, the distance is 25

so the slope is (25-10)/(15-0)=15/15=1

(I'm not sure what the units are; I can't really read the picture that well. I'm guessing it is 1 meter/second, or 3.6 km/ hour, or about 2.2 miles / hr)

at time 15, the distance is 25

then at time 25, the distance is 65

so the slope is (65-25)/(25-15)=40/10=4

at time 25 the distance is 65

at time 30, the distance is still 65

so the slope is (65-65)/(30-25)=0

finally, at time 30, the distance is 65

at time 40, the distance is 0

so the slope is (0-65)/(40-30)=-6.5

the speed here is actually positive 6.5

some explanation. Let's say I stand in one place. And you are standing 65 m away from me. And in 10 seconds, you are now in the same place as I am. Then you went from being 65 m away, to being 0 m away. So your distance from me change by -65 m. But you ran a distance of 65 m, not a distance of -65.

So, the graph would look like:

Note the open circles: the speed isn't actually defined at those spots. At the very instant when t=15 seconds, and you instantaneously change from going 1 m/s to 4 m/s, at that moment, the speed isn't defined

Is this how the graph for 1.a) should look like, because if so there is supposed to be 2 graphs for 1.a).