Example 11.7 - Chapter 11 Class 9 - Work and Energy

Last updated at August 14, 2026 by

Example 11.7 - Two girls, each of weight 400 N climb up a rope through - Examples from NCERT Book

part 2 - Example 11.7 - Examples from NCERT Book - Chapter 11 Class 9 - Work and Energy - Class 9

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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

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