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Thread: relative displacement

  1. #1
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    relative displacement

    port A is 80 km due north of port B. the sailing time from A to B is 5 hours. if the velocity of the current west is 12 km hr^-1 find the velocity with which the ferry should head in order to complete the journey in the scheduled time

    i have came up with only 1 equation. 80/vcosa =5 im now trying to find another equation with the current velocity in it and solve these 2 equations
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  2. #2
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    Re: relative displacement

    sketch a vector diagram ...
    Attached Thumbnails Attached Thumbnails relative displacement-velocity_vectors.jpg  
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    Re: relative displacement

    If you multiply both sides of that equation by v cos(a) you get 5vcos(a)= 80, an equation for the vertical distance traveled. Set up a similar equation for the horizontal distance traveled. If you want to end up at port B, the horizontal distance traveled must be 0.
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    Re: relative displacement

    so i did vsina-12=0 because horizontal distance traveled is 0 and than i subbed in v=80/5cos a and got 36.87 degrees
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    Re: relative displacement

    Quote Originally Posted by markosheehan View Post
    so i did vsina-12=0 because horizontal distance traveled is 0 and than i subbed in v=80/5cos a and got 36.87 degrees
    36.87 degrees relative to what?

    Velocity is direction & speed ... what speed should the ferry make good through the water?
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