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!

Physics 11 question - its probs rly easy

  1. Dec 9, 2008 #1
    Physics 11 question -- its probs rly easy !!

    1. The problem statement, all variables and given/known data

    A horizontal force applied to a 7.0 kg object initially at rest causes it to accelerate uniformly and travel a distance of 21m in 4.2s. What is the change in momentum of the object?

    2. Relevant equations

    p = mv

    3. The attempt at a solution

    Heres what i did but got it wrong:

    p=mv
    =(7.0kg)(0 m/s)
    = 0
    p=mv
    =(7.0kg)(5m/s)
    = 35

    so the answer should be 35 ya?
    but the answer in the back of the book is 70 kg x m/s
    help??
     
  2. jcsd
  3. Dec 9, 2008 #2

    PhanthomJay

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Re: Physics 11 question -- its probs rly easy !!

    You mistakenly considered its final velocity to be 5m/s. That is it's average velocity computed over the 21 meter distance in 4.2 seconds. What is its final velocity after 4.2 seconds?
     
  4. Dec 9, 2008 #3

    rl.bhat

    User Avatar
    Homework Helper

    Re: Physics 11 question -- its probs rly easy !!

    Check the calculation of the final velocity.
     
  5. Dec 9, 2008 #4
    Re: Physics 11 question -- its probs rly easy !!

    how do you find final velocity then?
     
  6. Dec 9, 2008 #5
    Re: Physics 11 question -- its probs rly easy !!

    You will need to use a kinematic equation to find the final velocity.
     
  7. Dec 9, 2008 #6

    rl.bhat

    User Avatar
    Homework Helper

    Re: Physics 11 question -- its probs rly easy !!

    Distance = Average velocity * time
    Average velocity = (u + v)/2
     
  8. Dec 9, 2008 #7
    Re: Physics 11 question -- its probs rly easy !!

    so once i have the average velocity how do i find th final velocity?
     
  9. Dec 9, 2008 #8
    Re: Physics 11 question -- its probs rly easy !!

    Think about what the average velocity actually is. It is an average of two velocities together. What are those two velocities?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Physics 11 question - its probs rly easy
Loading...