confusing physics problem?

A ball is dropped from a cliff and 2 seconds later, a second ball is thrown vertically downward. What must be the initial velocity of the second ball if it overtakes the first ball as it passes 400 meters?

Comments

  • The distance each ball falls is the same:

    ½g*t² = Vi*(t - 2) + ½g(t - 2)²

    t = time for ball 1 to fall 400 m = √(2y/g) = 9.035 sec

    Solving the above eq for Vi →

    Vi = 2g(t - 1)/(t - 2). Using the value of t computed above,

    Vi = 22.386 m/s

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