Check sibling questions

Ex 6.1, 2 - Volume of a cube is increasing at 8 cm3/s. How fast

Ex 6.1,2 - Chapter 6 Class 12 Application of Derivatives - Part 2
Ex 6.1,2 - Chapter 6 Class 12 Application of Derivatives - Part 3
Ex 6.1,2 - Chapter 6 Class 12 Application of Derivatives - Part 4
Ex 6.1,2 - Chapter 6 Class 12 Application of Derivatives - Part 5

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Ex 6.1, 2 The volume of a cube is increasing at the rate of 8 cm3/s. How fast is the surface area increasing when the length of an edge is 12 cm?Let 𝒙 be length of side V be Volume t be time per second We know that Volume of cube = (Side)3 V = 𝒙𝟑 Given that Volume of cube is increasing at rate of 8 cm3/sec. Therefore 𝒅𝑽/𝒅𝒕 = 8 Putting V = 𝒙𝟑 (〖𝑑(𝑥〗^3))/𝑑𝑡 = 8 〖𝑑𝑥〗^3/𝑑𝑡 . 𝑑𝑥/𝑑𝑥 = 8 〖𝑑𝑥〗^3/𝑑𝑥 . 𝑑𝑥/𝑑𝑡 = 8 3𝒙𝟐 . 𝑑𝑥/𝑑𝑡 = 8 𝒅𝒙/𝒅𝒕 = 𝟖/〖𝟑𝒙〗^𝟐 Now, We need to find fast is the surface area increasing when the length of an edge is 12 centimeters i.e. 𝒅𝑺/𝒅𝒕 for x = 12 We know that Surface area of cube = 6 × Side2 S = 6𝑥2 Finding 𝒅𝑺/𝒅𝒕 𝑑𝑆/𝑑𝑡 = (𝑑(6𝑥^2))/𝑑𝑡 = (𝑑(6𝑥2))/𝑑𝑡 . 𝑑𝑥/𝑑𝑥 = 6. (𝑑(𝑥2))/𝑑𝑥 . 𝑑𝑥/𝑑𝑡 = 6 . (2x) . 𝑑𝑥/𝑑𝑡 = 12𝑥 . 𝒅𝒙/𝒅𝒕 = 12𝑥 . 𝟖/𝟑𝒙𝟐 = 𝟑𝟐/𝒙 For 𝑥= 12 cm 𝑑𝑆/𝑑𝑡 = 32/12 (From (1): 𝒅𝒙/𝒅𝒕 = 𝟖/(𝟑𝒙^𝟐 )) 𝑑𝑆/𝑑𝑡 = 8/3 Since surface area is in cm2 & time is in seconds, 𝒅𝑺/𝒅𝒕 = 𝟖/𝟑 cm2 /s

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.