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!

Homework Help: Bullet, block, spring (again)

  1. Apr 28, 2009 #1
    1. The problem statement, all variables and given/known data
    A rifle bullet of mass 7.2 grams strikes and embeds itself in a block with mass 0.819 kg that rests on a frictionless horizontal surface and is attached to a coil spring. The impact compresses the spring 17 centimeters. Calibration of the spring shows that a force of 0.68 newtons is required to compress the spring 0.31 cm. Find the magnitude of the block’s velocity just after impact. Give your answer in m/s to the first decimal place.

    2. Relevant equations

    3. The attempt at a solution
    I have looked at at least 4 other posts on this forum about this question, but I still cannot quite get it.

    m1v1 = (m1+m2)v2

    Using some dimensional analysis, I get that force is equal to some 37 N. Multiply this with the 17 cm, and you get the work done on the spring. This is equal to .5 * m * v1^2. Solve this for V1, plug back into the momentum equation to get V2. Is this not correct because my answer differs from the solution.
  2. jcsd
  3. Apr 28, 2009 #2
    Ok, so I finally found the solution, and it's something pretty stupid that I never thought of. k the spring constant is given, then everything else is simple.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook