Slide11.JPG

Slide12.JPG

 

  1. Class 9
  2. Chapter 11 Class 9 - Work and Energy

Transcript

Example 11.7 Two girls, each of weight 400 N climb up a rope through a height of 8 m. We name one of the girls A and the other B. Girl A takes 20 s while B takes 50 s to accomplish this task. What is the power expended by each girl? Weight of each girl = mg = 400 N Height climbed by each girl = h = 8 m Power = (๐‘Š๐‘œ๐‘Ÿ๐‘˜ ๐‘‘๐‘œ๐‘›๐‘’)/(๐‘‡๐‘–๐‘š๐‘’ ๐‘ก๐‘Ž๐‘˜๐‘’๐‘›) And Work done = Force ร— Distance = m ร— g ร— h Girl A Power = (๐‘Š๐‘œ๐‘Ÿ๐‘˜ ๐‘‘๐‘œ๐‘›๐‘’)/(๐‘‡๐‘–๐‘š๐‘’ ๐‘ก๐‘Ž๐‘˜๐‘’๐‘›) = (๐‘š ร— ๐‘” ร— โ„Ž)/๐‘ก = (400 ร— 8)/20 = 20 ร— 8 = 160 W Girl B Power = (๐‘Š๐‘œ๐‘Ÿ๐‘˜ ๐‘‘๐‘œ๐‘›๐‘’)/(๐‘‡๐‘–๐‘š๐‘’ ๐‘ก๐‘Ž๐‘˜๐‘’๐‘›) = (๐‘š ร— ๐‘” ร— โ„Ž)/๐‘ก = (400 ร— 8)/50 = 8 ร— 8 = 64 W Thus, Power expended by Girl A is 160 W Power expended by Girl B is 64 W

About the Author

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Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.