# i can't detect what wrong have i done in a kinematics problem [closed]

a question was given to us in assignment which was as follows

A person moves 20 metres towards north then 30 metres towards east and then moves 30 x 1.414 metres towards south west. The whole trip takes 5 seconds. What is the person's average velocity for this whole journey?

i just squared every magnitude of velocity in all the three directions and then I took square root of that sum

doing so what i got is this number 55.735267112 so this will be the total displacement of that person and dividing this with the given time [5in this case] we get the answer as 11.1 but the answer is 2 m/s

can any one suggest me where is my concept going wrong

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## closed as off-topic by John Rennie, BMS, Ali, Brandon Enright, David Z♦Jul 6 '14 at 22:25

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The problem as written isn't very clear. You just gives directions and distance and no time so no velocities can be found. – jkeuhlen Jul 6 '14 at 16:18
but this is the only information given in the question – agha rehan abbas Jul 6 '14 at 16:20
@jkeuhlen i think distances and time would be enough for us to calculate the average velocity – agha rehan abbas Jul 6 '14 at 16:21
You have distance and then you have a time to stop. That time would be used to find acceleration. You would need time to cover the distance to get a speed. – jkeuhlen Jul 6 '14 at 16:23
@jkeuhlen yes time is given and it is 5secs in this case – agha rehan abbas Jul 6 '14 at 16:24

## 1 Answer

If you draw the path, it looks like this:

The person moved 10 m in 5 seconds.

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how can you say that he moved 10 metre in 5 seconds as there is no evidence for it – agha rehan abbas Jul 6 '14 at 16:25
Look at the vectors. The distance from the endpoint to the starting point is 10 m. – LDC3 Jul 6 '14 at 16:25
+1 for the drawing getting the point across better than any calculation – ACuriousMind Jul 6 '14 at 16:26
@agharehanabbas The person has a total displacement of 10 metres south. Velocity is the displacement per time. – jkeuhlen Jul 6 '14 at 16:27
@jkeuhlen yup got it and thanks for that edit – agha rehan abbas Jul 6 '14 at 16:29