calculus HELP!

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A person stands on a bridge that is 100 feet above a river.

If she drops a pebble how fast is it moving after 2 seconds?
How long does it take the pebble to reach the river below?
She has another pebble that she tosses up with initial speed of 8 feet per second. It goes up, then starts falling down to the river below. By the time it reaches the river what is its speed?

  • calculus HELP! -

    Calculus? Hardly.

    vf=vi+gt for the firstquestion

    second question: h=vi*t-4.9t^2 Vi=0, solve for t

    third question
    hf=hi+vi*t-4.9t^2
    0=100+8t-4.9t^2
    solve for time t, then vf=vi-9.8t

    but there is an easier method for the last:
    vf^2=vi^2+2ad where a=-9.8, d=-100

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