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quick physics question

A man cycles to work with the wind at 8.0 m/s and returns home against the wind at 4 m/s. What is his average speed? (hint:It is not 6 m/s)

I'm probably missing something obvious ?
thanks

Reply 1

cardine92

are you sure it's speed and not velocity?

Reply 2

chris2pyle

cardine92

are you sure it's speed and not velocity?

100% lol
thats why im confused. any ideas ?

5.3 ms-1

want to know why or want to work it out your self?

Reply 5

chris2pyle

Katermerang

want to know why or want to work it out your self?

whyy please? :smile:

Reply 6

Katermerang

Ok well lets write down the basics first:

Speed= Distance/time

Distance = d
Time to work=T1
Time back = T2

so you can write two equations form this data to work out the two individual speeds (to work and back)

8= d/T1 and 4= d/T2

Now Average speed = total distance/total time

so a rearrangement of the top equations gives:

Average speed = [2d] / [ (d/8) + (d/4)]

The "d"s cancel out leaving you with (16/3) or 5.3ms-1