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Bored
Lv 7
Bored asked in Science & MathematicsPhysics · 1 decade ago

freely falling bodies ?

A ball is thrown straight upward and rises to a maximum height of 25 m above its launch point. At what height above its launch point has the speed of the ball decreased to one-half of its initial value?

did they give me enough info? i can't figure this out.

5 Answers

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  • Anonymous
    1 decade ago
    Favorite Answer

    Working formula is

    Vf^2 - Vo^2 = 2gh

    where

    V = final velocity = velocity of ball at its max height = 0

    Vo = initial velocity

    g = acceleration due to gravity = 9.8 m/sec^2 (constant)

    h = maximum height attained by ball = 25 m (given)

    Substituting values,

    0 - Vo^2 = 2(-9.8)(25)

    NOTE the negative sign attached to the acceleration due to gravity. It simply means that the ball loses its speed as it goes up.

    And, solving for Vo,

    Vo = 22.14 m/sec.

    Let

    s = height where the speed of the ball is half of its original value

    and using the same formula above,

    Vf^2 - (22.14)^2 = 2(-9.8)(s)

    Since Vf = (1/2)(22.14) = 11.07, then the above simplifies to

    (11.07)^2 - (22.14)^2 = -19.6(s)

    and solving for "s"

    s = 18.75 m.

    Hope this helps.

  • Retsum
    Lv 6
    1 decade ago

    We can find the launch speed from

    v^2 - u^2 = 2as

    At max height v = 0

    -u^2 = -2g x 15

    u = SQRT(50g)

    Now v = (1/2)u = (1/2)SQRT(50g)

    From v^2 - u^2 = 2as

    s = (v^2 - u^2)/-2g = -[(3/4) x 50]/-2 = 18.75 m

  • Anonymous
    7 years ago

    Hey,

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    it's a perfectly working link!

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    It's a great game.

  • 1 decade ago

    Yes. Figure forwards to get original velocity then backwards to get height

    d = 0.5 AT^2

    25 = 0.5 * 9.8 m/s^2 * T1^2 solve for T1

    Then

    V = AT1

    V1 = 9.8 * T (from above) Solve for V1

    V2 = V1/2 Solve for V2

    V2 = AT

    V2 = 9.8 * T2 solve for T2

    d2 = 0.5 * A*T2^2 Solve for d2

    d2 = 0.5*9.8*T2^2

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  • ?
    Lv 4
    5 years ago

    equation v^2=u^2+2as preliminary velocity u=0, then v^2=2gh(a=g,s=h) at top h, permit v be the fee then v^2=2gh .........eq a million at some top h1,it somewhat is velocity 2v strengthen into doubled then (2v)^2=2gh1 4(v^2)=2gh1 by making use of eq a million 4(2gh)=2gh1 cancelling 2g we get h1 =4h

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