Maths-
General
Easy

Question

A spherical balloon is being inflated at the rate of 30c c to the power of blank divided by m i n. The rate of increase of the surface area of the balloon when its diameter is 14cm, is

  1. 7 sq cm/min  
  2. 10 sq cm/min  
  3. 17.5 sq cm/min  
  4. 28 sq cm/min  

The correct answer is: 10 sq cm/min


    Let volume of sphere(V)=fraction numerator 4 over denominator 3 end fraction pi r to the power of 3 end exponent
    rightwards double arrow fraction numerator d V over denominator d t end fraction 4 pi r to the power of 2 end exponent fraction numerator d r over denominator d t end fraction blank rightwards double arrow fraction numerator d r over denominator d t end fraction equals fraction numerator 35 over denominator 4 pi r to the power of 2 end exponent end fraction

    Let surface area of sphere(S)equals 4 pi r to the power of 2 end exponent

    rightwards double arrow fraction numerator d S over denominator d t end fraction equals 2 cross times a pi r fraction numerator d r over denominator d t end fraction

    blank equals 2 cross times 4 pi r cross times fraction numerator 35 over denominator 4 pi r to the power of 2 end exponent end fraction

    therefore blank fraction numerator d S over denominator d t end fraction equals 10 s q blank c m divided by m i n

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