1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

SAT Subject Test in Physics

  1. May 24, 2008 #1
    [SOLVED] SAT Subject Test in Physics

    1. The problem statement, all variables and given/known data
    Assume that every projectile fired from a toy cannon experiences force F along the length of the barrel. If a projectile of mass M leaves the barrel with speed, V, at what speed will a projectile of mass 2M leave the barrel with?

    2. Relevant equations
    F=ma, a=(Vf-Vo)/t

    3. The attempt at a solution
    The force F, produces acceleration of V/t for mass m, so the same force should produce F=(2m)(v/t), so the velocity equals v/2?

    This is a multiple choice question with choices A) v/2, B)v/sqrt(2), C)v, D)2v, E)4v

    The book says the answer is B, but gives no explanation.
  2. jcsd
  3. May 24, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Careful: The time in the barrel is not the same for the two projectiles.
  4. May 24, 2008 #3
    Oh, thats true, so how can I get around that?
  5. May 24, 2008 #4

    Doc Al

    User Avatar

    Staff: Mentor

    How do the accelerations compare? How does final speed (at the end of the barrel) depend on distance and acceleration?
  6. May 24, 2008 #5
    The final speed is Acceleration/Distance, and we know the distance must be the same for both objects. Can we rearrange the v=a/d and substitute it into F=ma?
  7. May 24, 2008 #6
    Wait, v doesn't equal a/d, I don't know what I'm thinking...
  8. May 24, 2008 #7
    Oh, I found out how to do it, just use v^2=2ad and work it out.

    EDIT: Sorry for the obnoxious triple post.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: SAT Subject Test in Physics
  1. SAT Subject Test (Replies: 10)

  2. SAT physics help? (Replies: 2)

  3. SAT physics question (Replies: 3)