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Math Help - Velocity of a Ball

  1. #1
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    Velocity of a Ball

    A small rubber ball is thrown into the air by a child at a velocity of 20 feet per second. the child releases the ball 4 feet above the ground. What is the velocity of the ball after 1 second?
    modeled by: s(t)=-16t^2+v0t +s0 where v0 is the velocity and s0 is the vertical position of object at time t=0....HUH?

    I need help on how to set up. TY!
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  2. #2
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Snarfsnarf2006 View Post
    A small rubber ball is thrown into the air by a child at a velocity of 20 feet per second. the child releases the ball 4 feet above the ground. What is the velocity of the ball after 1 second?
    modeled by: s(t)=-16t^2+v0t +s0 where v0 is the velocity and s0 is the vertical position of object at time t=0....HUH?

    I need help on how to set up. TY!
    I assume you are in a Calculus class. The velocity is the first time derivative of the position function.

    -Dan
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    further info needed on velocity of a ball

    I'm sorry, but I don't understand your statement. Could you kindly explain? Sadly, yes, I'm in calculus...it makes no sense to me.
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    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Snarfsnarf2006 View Post
    I'm sorry, but I don't understand your statement. Could you kindly explain? Sadly, yes, I'm in calculus...it makes no sense to me.
    s(t) is your position function.

    v(t) = \frac{ds}{dt} is your velocity function. Take the derivative of s(t) to get v(t) and plug in t = 1.

    Or are you saying you don't know how to do the derivative?

    -Dan
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    in response to

    both actually. My brain just doesn't seem to grasp math. Particularly w/letters and #'s. Sorry to be a pest.
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  6. #6
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Snarfsnarf2006 View Post
    both actually. My brain just doesn't seem to grasp math. Particularly w/letters and #'s. Sorry to be a pest.
    You aren't being a pest. I'm just worried for you in your class. You really need to speak with your teacher about this.
    s_0 = 4 and v_0 = 20, so

    s(t) = -16t^2 + 20t + 4

    v(t) = -32t + 20

    Thus at t = 1:
    v(1) = -32 \cdot 1 + 20 = -12

    So the velocity is 12 ft/s downward.

    Please tell me/us all what you don't understand in the above, if anything.

    -Dan
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