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: How can i solve this using Bernoulli rule

  1. Sep 12, 2009 #1
    http://up2.up-images.com/up//uploads2/images/hosting-036ee42f15.jpg [Broken]

    in the figure, which ball will win in the race?
    note: there is no energy loss
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 12, 2009 #2
    You can use logic to solve it. For example provided curves are the same (obvious) divide them in to two parts, then its clear that the upwards one will last more than the downwards and then the bump ball will have speed so it'll need less time tha the other to complete the second part of the curve. This is what my intuition tells me but I think that it can be proved I do I tell you.

    Good science :)
  4. Sep 12, 2009 #3
    Hello sa ta.You have already given the answer.If there is no energy loss what does that tell you?
    Last edited by a moderator: May 4, 2017
  5. Sep 12, 2009 #4


    User Avatar
    Homework Helper

    Length of dip and bump is the same.
    But A moves faster in the dip and B moves slower on the bump. So A wins the race.
  6. Sep 13, 2009 #5
    thanks for all .. but i need the right answr today plz??
    A or B wins the race? and why??

    Dadface: can u answer ur question "If there is no energy loss what does that tell you?"
  7. Sep 13, 2009 #6
    There is a KE to KE change as the balls cross the bump and the hill. The KE gained by A on the way down is lost on the way up and the KE lost by B on the way up is gained on the way down,from this we conclude that the balls travel with the same steady speed on the flat portions.Now consider the average speed of the balls on the bump and in the dip as explained by ri.bhat,for example why does A get to the bottom of the dip faster than B gets to the top of the hill?What can you then say about the average times for the whole journey?
    Last edited: Sep 13, 2009
  8. Sep 13, 2009 #7
    so, from ur explanation A and B wins and reach at the same time?
  9. Sep 13, 2009 #8
    No, A wins.Consider the change of speed of A as it moves to the bottom of the dip and then rises to the top again .Now consider the change of speed of B as it rises to the top of the bump and then falls.Now compare the two and you should see that the average speed of A in the dip is greater than the average speed of B over the bump.
  10. Sep 14, 2009 #9
    thanks a lot
    now i understand what did u mean
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook