1. Not finding help here? Sign up for a free 30min 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!

Momentun And Collisions

  1. Jul 22, 2003 #1

    sb

    User Avatar

    1. An experiment is performd in a physics laboratory to find the mass of a stationary particle, B. A proton, A, of mass 1.7 x 10^-27 kg, travelling at 4.0 x 10^6 m/s, strike B and bounces straight back at a speed of 2.0 x 10^6 m/s. If B moves ahead at 1.0 x 10^6 m/s. calculate B's mass

    2. Two, studends, C and D, are facing each other on "friction-less" roller skates. C has a mass of 80kg and D has a mass of 50kg. Now they push each other and D acquires a velocity of 4.4m/s [W]. What velocity does C acquire?
     
  2. jcsd
  3. Jul 22, 2003 #2
    Hi sb,
    could you please tell us what you have got so far, and where you are stuck.
     
  4. Jul 22, 2003 #3

    sb

    User Avatar

    ummmm i am very very very confused. Plz kindly show me how u wud go about solving this question. It wud be very helpful and appreciated and i will be very thankful.
     
  5. Jul 22, 2003 #4

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Sorry, but that is not the policy of this Forum. I placed a note at the top of the Homework Help Forum called Read This Before Posting. Please do read it. :smile:

    Actually, it would most likely not be helpful to you at all. If we simply show you how to do the problem, then you really aren't learning anything.

    You should have learned about the law of conservation of momentum in your class. Come on, give these a shot. At least try to set them up. They really are very easy problems.
     
  6. Jul 22, 2003 #5

    sb

    User Avatar

    atlest give me a clue sir...
     
  7. Jul 23, 2003 #6

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    Okay, here's clue: look up the definition of "momentum" and the law of "conservation of momentum" in your text book

    Calculate the momentum of each particle, before and after the collision and post them here. Then we will be able to help you further.
     
  8. Jul 23, 2003 #7

    Doc

    User Avatar

    Unless this guy has posted in another thread, I can't say he is even using a textbook (even though it is in homework help). We seem to assume all of the time that these people are students. He might not be. I post here, I'm not a student. Hell, someday I might even post a question!
     
  9. Jul 23, 2003 #8

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    OK, then he can look up "conservation of momentum" up in HyperPhysics, one of the many helpful resources I posted at the top of the Homework Help Forum.

    OK, but if you post it in my Forum, then you had better show your work first. :smile:
     
  10. Jul 23, 2003 #9

    sb

    User Avatar

    One kg of fat is equivalent to about 30 MJ of energy. The efficiency of converting fat to mechanical energu is about 20%.
    a. Suppose you lift a mass of 12kg 2.0m vertically, 500 times how much work do you do? (Assume that the work done by mass on you is disepated as heat to the surroundings).
    b. If asll the enery used to do the work comes from "burning" fat, how much fat is used up by the expercise

    This is what I did:
    1kg = 30MJ
    percentage efficinecy = 20%
    m = 12kg
    delta d= 2.0m
    w=?

    1kg = 1,000,000J
    12kg = 12,000,000J
    E = 12,000,000J
    IMA = 12,000,000J

    potencial efficiency = (AMA/IMA) * 100%
    20% = (AMA/12,000,000) * 100
    AMA = (20/100) * 12,0000
    AMA = 24000J

    FBD Diagam

    Eg = mgh
    Eg = (12kg)(9.8m/s^2 [D])(2.0)
    Eg = 235.2N

    Answers for this problem given at the end of the book are
    a. 1.2x10^2 kJ
    b. 20g
     
  11. Jul 23, 2003 #10

    sb

    User Avatar

    sorry about that message above, clicked the wrong button, thanks a lot for all your help
     
  12. Jul 23, 2003 #11

    Doc

    User Avatar

    That's the thing though. I suspect that MOST of the people that could answer the type of question I would ask hang out here. That includes YOU Tom. The type of question I would ask would most likely concern the type of problem where I couldn't show any work at all. That would be my point in asking. I agree with the policy of showing your work but sometimes it is not possible. Kind of a catch 22. I guess I won't expect much. Too bad, considering the seemingly high level of intelligence in here.
     
  13. Jul 24, 2003 #12

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    Doc said

    Have you considered posting such questions in the "mathematics" and "physics" sections rather than the "Homework Help" section?
     
  14. Jul 24, 2003 #13

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    It is always possible.

    If a student has studied and absorbed the material to any extent, he will at least have an incling as to the starting point of the problem. Homework problems are not designed to be masochistic. Certainly they are meant to be met with some strain, but they can all be done with some effort.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Momentun And Collisions
  1. Angular momentun (Replies: 1)

Loading...