Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Midterm Study Guide help

  1. Jan 6, 2008 #1
    1.) A stone is thrown with an initial velocity of 7.0m/s. the acceleration of the stone is constant and has the value of -9.8m/s to the power of ((2)). What is the velocity of the stone after .50 s?

    I put 2.1 not sure if it's right.


    2.) An airplane starts from rest and accelerates at 10.8 m/s to power of ((2)). What is its speed at the end of a 400m long runway.

    I don't really know where to begin.

    3.) A displacement vector is 34.0m in length and is directed 60.0 degrees east of north. What are the components of this vector?

    Again I don't even know where to begin.

    It would be nice if someone could explain these to me. Thanks in advance.

    Alksjadf
     
  2. jcsd
  3. Jan 6, 2008 #2

    Kurdt

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    For question 1.) you are correct but remember your units.

    For 2 you will need another of the kinematic equations which can be found here.

    https://www.physicsforums.com/showpost.php?p=905663&postcount=2

    Remember what information you're given and what you need, that will help you choose.

    For 3.), think of the vecto as the hypotenuse of a right angled triangle the components are the lengths of the other two sides in the north and east directions. How would you find the lengths of two sides of a right angled triangle given the hypotenuse and an angle?
     
  4. Jan 6, 2008 #3
    Oh ok so for number 3 i would have to use sin 60 = dy/34 and cos 60 = dx/34.

    And for 2 I'm not sure what equation to use is the velocity and displacement the right one?

    [tex]v^2 = v_0^2 + 2 a \Delta x[/tex]
     
  5. Jan 6, 2008 #4

    Kurdt

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Your cos and sin will be the other way round because the angle is measured from the y-axis (north).

    Yes you could use the equation you've stated for 2.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook