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.

  2. jcsd
  3. Jan 6, 2008 #2


    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.


    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


    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