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!

Question on the free-fall of 2 bodies

  1. Oct 29, 2016 #1
    1. The probleas
    statement, all variables and given/known data

    Two stones are projected from the top of a tower 100m high each with velocity of 10m/s. One is projected upward while the other is projected downward. Find the ratio of velocity's by with which they strike the ground.

    2. Relevant equations
    S= ut +1/2(a)(t)^2
    (v)^2-(u)^2=2as
    v=u+at




    3. The attempt at a solution
    Let the stone projected upward be , body A
    And the body projected downward be body B

    For body A
    (v)^2-(u)^2=2as
    (v)^2-(100)=2(10)(100)
    v=√(1900)
    For body B before reaching max. height
    (v)^2-(u)^2=2as
    -(100)=(2)(10)(s)
    5=s
    For body B after reaching the max. height
    (v)^2-(u)^2=2as
    (v)^2=(2)(10)(105)
    v=√(2100)

    And I reached a dead end because
    (10)(√21)/(10)(√19)

    Ain't in the options
    Please help
     
  2. jcsd
  3. Oct 29, 2016 #2

    PeroK

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Maybe you could do this without using any equations?
     
  4. Oct 29, 2016 #3
    OK lemme see
     
  5. Oct 29, 2016 #4
    But the distance travelled by both the bodies is different
     
  6. Oct 29, 2016 #5

    PeroK

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Try describing the motion of the ball that gets thrown up. Do you notice anything?
     
  7. Oct 29, 2016 #6
    OK wait a sec
    Is it that the second body gains the same velocity as the first on whenn it is100m high
     
  8. Oct 29, 2016 #7

    PeroK

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You mean if you throw a ball up at 10m/s, you know what speed it has when it comes back down to its starting point?
     
  9. Oct 29, 2016 #8
    v=u+at (before reaching its highest point)
    0=10+10t
    1=t
    Then it would take 1s to come back to its starting point and
    v=u+at( after reaching the highest point)
    v=10m/s
    So basically both bodies start from the same point with the same vel. So the velocity before reaching the ground would be the same hence the answer is 1:1
     
  10. Oct 29, 2016 #9
    Thanks for the help:wink:,
     
  11. Oct 29, 2016 #10

    PeroK

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Yes, exactly. But, you may wish to go back to your equations and figure out how you got the wrong answer!

    Hint: ##s## in the suvat equations is "displacement", not "total distance travelled".
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Question on the free-fall of 2 bodies
  1. Free falling body (Replies: 3)

  2. Free Falling bodies (Replies: 5)

Loading...