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Help with physics

  1. Sep 25, 2006 #1
    So my Physics teacher assigned us 15 problems and these are 3 that i have not been able to figure out, i've been trying to do these for over an hour and a half.

    A bird watcher meanders through the woods, walking 1.48 km due east, 0.269 km due south, and 2.10 km in a direction 62.3 ° north of west. The time required for this trip is 0.9342 h. Determine the magnitudes of the bird watcher's (a) displacement and (b) average velocity.

    ok so so i'll be using R^2= deltax^2+deltay^2

    but i dont know what to do with the northwest one

    A car drives horizontally off the edge of a cliff that is 63.3 m high. The police at the scene of the accident note that the point of impact is 146 m from the base of the cliff. How fast was the car traveling when it drove off the cliff?

    I need to find the time it tkaes to hit the ground using delta x=v0t+1/2atsquared, then 146/t and thats my velocity, think

    but i dotn know if V0 is zero or not

    An eagle is flying horizontally at 6.4 m/s with a fish in its claws. It accidentally drops the fish. (a) How much time passes before the fish's speed doubles? (b) How much additional time would be required for the speed to double again?

    I honestly do not have a clue about this one

    Any help would be appreciated
    Last edited: Sep 25, 2006
  2. jcsd
  3. Sep 25, 2006 #2
    Try drawing really big pictures and see if that helps. I don't know where to start giving advice if you can't say what your troubles or initial thoughts are.
  4. Sep 25, 2006 #3

    K, i tried to clear it up a bit
  5. Sep 25, 2006 #4
    Alright, so you are on the right track for the first one. So, the magnitudes of the first couple are pretty easy to find because they only have one component. To find the magnitude of the other northwest displacement, you will have to resolve the vector into its components, that is how much it moves left and how much it moves up. You can find these components using trigonometry. The average velocity part of the question might trip you up, so remember that velocity deals with total displacement - meaning that running forward 10m and then backward 10m is 0 velocity.

    For this second problem, yes you are absolutely right that you need to find the time it takes for the car to travel the trajectory. I think you got a little confused though. What do you know about the car's intial velocity in the y direction, the instant it drives off how fast is it moving downwards? The time I got was 3.6 if you want something to check with. You aren't finished there though, you will need to use the time you found again (hint: the car is pretty far from the edge).

    This last one might be a little tricky, but it isn't too bad. Think about the concepts. Will the fish's horizontal velocity ever change? What does change? Relativity actually seems like the best way to solve this, but you probably haven't gotten there yet. Also, it sort of helps to know Calc 1 just for some basic ideas. Having those said, which I assume aren't under your belt, using triangles will help a lot.
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