crystal 發問於 科學及數學數學 · 1 十年前

F.3 VOLUME問2

1. Air is leaking out from a sherical balloon.Find the % decrease in its volume when its surface area has decreased by 36%.

2.It is known that nearly 70% of the surface of the Earth are oceans.

The radius of the Earth is 6400km.Find the total area of the oceans on the Earth.

PLZ show the steps.

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  • 1 十年前
    最愛解答

    1

    let the radius of the original balloon is r1﹐the radius of the new balloon is r2

    surface area has decreased by 36%

    4*pi*r2^2=0.64*4*pi*r1^2

    r2^2/r1^2=0.64

    r2/r1=0.8

    the volume of new balloon /the volume of original balloon

    =(r2/r1)^3

    =0.8^3

    =0.512

    so the % decrease of volume of new balloon

    =1-0.512

    =0.488

    =48.8%

    2

    the radius of the Earth is 6400km

    the surface area of the Earth

    =4*pi*(6400)^2

    =514719744 km^2

    the total area of the oceans on the Earth.

    =0.7*514719744 km^2

    =360303820.8 km^2

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