Example 44 - A man of height 2 meters walks at uniform speed - Finding rate of change

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  1. Chapter 6 Class 12 Application of Derivatives
  2. Serial order wise
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Example 44 A man of height 2 meters walks at a uniform speed of 5 km/h away from a lamp post which is 6 meters high. Find the rate at which the length of his shadow increases. Let AB be the lamp post & Let MN be the man of height 2m. & Let AM = l meter & MS is the shadow of the man Let length of shadow MS = s Given man walks at speed of 5 km/h = 5km/h We need to find rate at which the length of his shadow increases. i.e. we need to find From (1) & (2) 6 1000 + = 2 1000 6 + = 2 6s = 2l + 2s 6s 2s = 2l 4s = 2l 2s = l l = 2s We need to find Diff w.r.t t = 2 = 2. 5 = 2 = 5 2 So, = km/hr.

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Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.