Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A dog's position along a straight path is plotted against time. The graph is three straight pieces joining these points:
| (s) | ||||
|---|---|---|---|---|
| (m) |
On a position-time graph, the slope of each straight piece is the velocity there; a flat piece means rest. Average velocity uses the first and last points; average speed adds the lengths of every piece.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The three slopes. to : . to : flat, . to : .
Step 2. Average speed. Path length , so .
Step 3. Average velocity. .
Answer: (a) , and . (b) and .
Check. The dog ends behind its start, so the average velocity is small and negative.
Watch out. The rest from to still counts in the time for both averages.
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