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A man of height 1.8m walks away from a lamp at a height of 6m. if the man’s speed is 7m/s , the speed in m/s at which the tip of the shadow moves is A)5m/s B)7m/s C)10m/s D)17m/s
A man of height 1.8m walks away from a lamp at a height of 6m. if the man’s speed is 7m/s  , the speed in m/s at which the tip of the shadow moves  is A)5m/sB)7m/sC)10m/sD)17m/s

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4 years ago

Vikas TU
14149 Points
```							The shadow triangle and the men’s triangle with lamp would be simlar.Hence let x be the distance of tip of the shadow from man and y be the distance of man from the lamp at any instant.Then,from similar triangles we get,1.8/x = 6(x+y)or7x = 3y........................................................(1) Now from distance – speed formulae:for man,7 = y/t => t = y/7 seconds.for shadow,v = (x+y)/t => t = (x+y)/vnow time would be same for both therfore,v = 7x/y + 7 from eqn. (1) we get,v = 3 + 7 => 10 m/s.
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4 years ago
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Course Features

• 110 Video Lectures
• Revision Notes
• Test paper with Video Solution
• Mind Map
• Study Planner
• NCERT Solutions
• Discussion Forum
• Previous Year Exam Questions