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: Find velocity and acceleration (positive or negative)

  1. Sep 15, 2014 #1
    What would the velocity and acceleration be if a person was tossing a ball upward but downward direction is positive? When the ball was falling down, what would the velocity and acceleration be?
  2. jcsd
  3. Sep 15, 2014 #2
    On the way up, your acceleration would be down (positive) and your velocity would be up (negative).

    Once the ball is falling, the acceleration is still down (positive) and the velocity is down (positive)
  4. Sep 15, 2014 #3
    ... Assuming there is gravity
  5. Sep 15, 2014 #4
    But wouldn't there be a difference since the downward direction is positive
  6. Sep 15, 2014 #5
    Oh wait,,, nvmm thxx
  7. Sep 15, 2014 #6
    Its also cool to note that even at the top of the motion, when the velocity is zero, the acceleration is still in the down (positive) direction.
  8. Sep 15, 2014 #7
    Oh yea,, its something like the acceleration cannot be 0 because if it is , it againsts the gravity ...something like that..right?
  9. Sep 15, 2014 #8
    Gravity is always accelerating the object. But the object has to stop before going backward (has to be 0 velocity). This is a really really really small time though.
  10. Sep 15, 2014 #9


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I assume you are talking about what happens after it leaves the mans hand while subject to gravity (eg not while he's actually throwing it).

    On the way up....

    The displacement is negative
    The velocity is negative
    The acceleration is positive

    After max height on the way down...

    The displacement is initially still negative but then it goes positive as it passes the origin.
    The velocity is positive
    The acceleration is positive
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted