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Homework Help: 2 Questions about motion in 1 direction

  1. Sep 23, 2015 #1
    So I have 2 questions to answer for my physics class and I'm not quite sure what to do. Here are the two questions and I was wondering if someone could possibly point me in the right direction. I'm not asking for the answers I just kind of want a rough idea of where to start. Thank you


    An athlete swims the Length L of a pool in a time t1 and makes the return trip to the starting position in a time t2. If she is swimming initially in the positive x-direction, determine her average velocities symbolically in

    (a) the first half of the swim,

    (b) the second half of the swim,

    (c) the round trip,

    (d) What is her average speed for the round trip?

    An object moves with constant acceleration 4.00 m/s2 and over a time interval reaches a final velocity of 12.0 m/s.
    (a) If its original velocity is 6.00 m/s, what is its displacement during the time interval?
    (b) What is the distance it travels during this interval?
    (c) If its original velocity is -6.00 m/s, what is its displacement during this interval?
    (d) What is the total distance it travels during the interval in part (c)?
  2. jcsd
  3. Sep 23, 2015 #2


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    Education Advisor
    Gold Member

    Hey Nick. Welcome to the forum.

    First, don't neglect the template. It's there for a reason.

    Second, what parts of this are you actually able to do? We are supposed to see you make some effort to do your homework and help you with small places you get stuck. But "I can't figure out how to start" isn't really all that good.

    If these questions are defeating you at the very start then you need to be doing more reading. Or possibly to go here and sign up.


    But here is some help anyway.

    1) Do you know what a vector is? Do you know the difference between a vector (such as velocity) and a scalar (such as speed)? A vector has a magnitude and a direction, like an arrow with a length. A scalar has only a magnitude. Do you know how to calculate the speed of an object that travels some distance in some time? Do you know how to calculate the velocity (a vector) for the same object? If the swimmer returns to her starting location, then something is zero. What is zero? But other things are not zero. What is not zero?

    2) To solve this problem you need to have studied constant acceleration in class. Or have read it from your text. Look for the part of your text that explains constant acceleration. You should see equations that look something like this.

    ##X(t) = X(0) + V(0) t + 1/2 A t^2##
    ##V(t) = V(0) + A t##

    Part a and b are pretty easily solved from that. For part c and d you are starting going to need to notice that you started out going in the negative direction. And remember the swimmer who did something the same. And remember the difference between a scalar and a vector.
  4. Sep 25, 2015 #3
    Thank you for your reply and I will try to be more careful when it down to following the template. After doing some searching in my book I managed to figure it out... I think.

    a) v= displacement/ time
    v= l/t1 in x direction

    b) V= displacement/ time
    v= l/t2 in -xdirection

    c)V= displacement/time
    V= 0/(t1+T2)

    a) v2 = V20 +2aXΔ
    (v2-v20)/2a = XΔ
    (122-62)/2*(4)= XΔ
    XΔ = 13.5

    b) 13.5

    c) v2 = V20 +2aXΔ

    d)(v2-v20)/2a = XΔ
    (02-(-6)2)/2*(4)= XΔ
    XΔ = -4.5

    13.5m + -4.5 = 22.5
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