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!

A rock from a boat - could you help me understand?

  1. Oct 19, 2012 #1
    1. The problem statement, all variables and given/known data

    A man on a boat throws behind him a rock of mass m1=2kg with a velocity of v1=18m/s. The mass of a man with a boat is m_2=90kg. What velocty v_2 will the boat go with?

    2. Relevant equations

    v2 = (m1*v1)/m2

    3. The attempt at a solution

    So I was upsent on the lesson where we were speaking about this and can't figure out where does the formula I wrote above come from. Why is it certain that m2v2=m1v1? Of course I know I can just plug the numbers inside and bam, I've got my answer but I'd rather know why does it work. Could you help?
     
  2. jcsd
  3. Oct 19, 2012 #2
    Well the eqaution implies that: mom boat - mom rock = 0
    Why would that be?
     
  4. Oct 19, 2012 #3

    Doc Al

    User Avatar

    Staff: Mentor

    It comes from the conservation of momentum. Since (presumably), the man and boat start out at rest, the total momentum is zero.

    You might want to read this: Momentum Conservation in Explosions
     
  5. Oct 19, 2012 #4
    Oh, I see. Thank you a lot!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: A rock from a boat - could you help me understand?
  1. Help me understand (Replies: 3)

  2. Help me to understand. (Replies: 1)

  3. Help me understand μ! (Replies: 2)

Loading...