Maths-
General
Easy

Question

If the semi-vertical angle of a cone is 45 degree, then the rate of change of volume of the cone is

  1. Curved surface area times the rate of change of r  
  2. Base area times the rate of change of l  
  3. Base area times the rate of change of r  
  4. None of these  

The correct answer is: Base area times the rate of change of l


    Let r be the radius of the base, h the height and l slant height of the cone with semi-vertical angle 45 degree. Then,
    r equals h and l to the power of 2 end exponent equals r to the power of 2 end exponent plus h to the power of 2 end exponent equals 2 r to the power of 2 end exponent

    Let V be the volume. Then,

    V equals fraction numerator 1 over denominator 3 end fraction pi r to the power of 2 end exponent h equals fraction numerator 1 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 equals pi r to the power of 2 end exponent fraction numerator d r over denominator d t end fraction equals A r e a blank o f blank t h e blank b a s e cross times fraction numerator d r over denominator d t end fraction

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