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Class 12
Solutions of Sample Papers and Past Year Papers - for Class 12 Boards

The most economical speed to run the train is:

(a) 18 km/h Β  (b)5 km/hΒ  (c) 80 km/h Β  Β Β Β Β Β (d) 40 km/hΒ 

Β 

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Question 48 The most economical speed to run the train is: (a) 18 km/h (b)5 km/h (c) 80 km/h (d) 40 km/h We need to find minimise Cost Now, Cost = C(v) = πŸ‘πŸ•πŸ“/πŸ’ 𝒗 + πŸ”πŸŽπŸŽπŸŽπŸŽπŸŽ/𝒗 Differentiating w.r.t v C’(v) = πŸ‘πŸ•πŸ“/πŸ’ βˆ’ πŸ”πŸŽπŸŽπŸŽπŸŽπŸŽ/𝒗^𝟐 Putting C’(v) = 0 0 = 375/4 βˆ’ 600000/𝑣^2 600000/𝑣^2 = 375/4 600000 Γ—4/375 = 𝑣^2 600000 Γ—4/375 = 𝑣^2 1600 Γ— 4 = 𝒗^𝟐 40 Γ— 2 = 𝒗 80 = 𝒗 𝒗 = 80 km/hr So, the correct answer is (c)

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Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths and Science at Teachoo.