A cyclist rides along a straight seafront: 750 m north in 150 s, then 300 m back south in 75 s.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A cyclist rides along a straight seafront: north in , then back south in .
- What is her average speed for the whole ride?
- What is her average velocity?
Need a reminder? The key ideaShow
Over a time :
Average speed is never negative; average velocity has the sign of the displacement.
The worked solution
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.
Given. north in ; south in .
Step 1. Whole time. .
Step 2. Average speed. .
Step 3. Average velocity. , north.
Answer: (a) . (b) north.
Check. Her speeds were and ; an average speed between them makes sense.
Watch out. Averaging the two speeds, , is wrong: she spent twice as long going north.
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