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Math Help - who can help me with this Q

  1. #1
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    who can help me with this Q

    Two spheres are cut from a certain uniform rock. One has radius 4.75 cm. The mass of the other is three times greater. Find its radius.
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  2. #2
    MHF Contributor
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    Quote Originally Posted by yzc717 View Post
    Two spheres are cut from a certain uniform rock. One has radius 4.75 cm. The mass of the other is three times greater. Find its radius.
    Same piece of rock of uniform density.
    density = (mass) / (volume)
    4/3*
    So, if density is constant or the same,
    (m1)/(V1) = (m2)/(V2)
    where V1 is volume of m1
    and V2 is volume of m2

    Given: m2 = 3*m1
    So,
    (m1)/(V1) = (3*m1)/V2
    1 /V1 = 3 /V2
    Cross multiply,
    V2 = 3*V1

    Let R = radius of m2,
    (4/3)pi(R^3) = 3[(4/3)pi(4.75)^3]
    R^3 = 3(4.75)^3
    R = (4.75)cubrt(3) cm -------answer.
    In decimals,
    R = 6.8507 cm -------answer also
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