Question

A seagull flies at a velocity of 9.00 m/s straight into the wind. (a) If it takes the bird 20.0 min to travel 6.00 km relative to the Earth, what is the velocity of the wind? (b) If the bird turns around and flies with the wind, how long will he take to return 6.00 km? (c) Discuss how the wind affects the total round-trip time compared to what it would be with no wind.

a) $-4.00 \textrm{ m/s}$

b) $462 \textrm{ s}$

c) see video for derivation

# OpenStax College Physics, Chapter 3, Problem 53 (Problems & Exercises)  In order to watch this solution you need to have a subscription.

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• Video Transcript
Hi blue, thanks again for the questions. At 3:25 $v_\textrm{ag}$ turns out to be negative, as you predicted. I think what you were expecting is to see a minus before the $v_\textrm{ag}$ term, but the negative is instead in the value of $v_\textrm{ag}$. The formula has only positives since it says "combine these velocities together" - which means add them. The $v_\textrm{ag}$ turns out to be negative, so adding $v_\textrm{ag}$ to $v_\textrm{sa}$ reduces $v_\textrm{sa}$. We have ended up adding a negative... yeah, I can see why this is confusing, but I hope this is helping.
At 3:40 I'm drawing $-v_\textrm{sa}$. The negative means draw $v_\textrm{sa}$ in the opposite direction.