I only have three variables

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

    Physics: Only three variables and I don't know how to solve?
    here is one problem: Heather and Jerry are standing on a bridge 50 m above a river. Heather throws a rock straight down with a speed of 20 m/s . Jerry, at exactly the same instant of time, throws a rock straight up with the same speed. Ignore air resistance. --- I need to find the time elapsed between the splashes.

    A rock is tossed straight up with a velocity of +20 m/s. When it returns, it falls into a hole 10m deep. ----I need to find velocity and time for the rock at the moment it reaches the bottom of the hole .

    For both of these I only have three variables, Velocity initial, change in X, and A. Should I assume that the V final is 0 in these?? otherwise I am confused. Thanks!!

    2. Relevant equations

    all 5 standard kinematics

    3. The attempt at a solution

    The questions is conceptual...currently i cannot attempt an answer as far as I know.
  2. jcsd
  3. You have 3 variables, not including one variable that you want to find (work out what this one is first!) Then go through your 5 equations and use the one that includes all 4. You might have to do some rearranging!
  4. verty

    verty 1,950
    Homework Helper

    The first of your questions is easier than it looks, if you see the trick...
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