On average, a mass of a book is about 0.5 kg and a year’s worth of “Tennis” maga

Question

On average, a mass of a book is about 0.5 kg and a year’s worth of “Tennis” magazines is 5 kg. You carry a dozen books from the ground level to the second floor stacks, 20 m above. You leave the books there and take two older bundles of “Tennis” down to the basement 10 m below the ground level. In the basement you picked up another 12 books and brought this final load to a 1 m tall desk desk on the ground floor. Neglect work of friction! What was the total work done by the gravity on the complete trip while you were carrying them around?

Explanation / Answer

dozen books = 12 total mass = 6kg first trip wrkdone by gravity = -6*g *20( since displacement is done oppsite to gravity, it is negative) second trip two bundles of tennis book = 5* 2 kg total displacement = 20 upto grond + 10 till basement work done by gravity = + 10*(20+10) *g (since displacement is done oppsite to gravity, it is +ve) third trip mass of books = 12*0.5 = 6kg total displacement = 10 upto ground floor + 1 m tall desk = 11 work done by gravity = -6*11*g ( since displacement is done oppsite to gravity, it is negative) total work by gravity = g*( -120+300-66) = 114*g =1117.2 Joules

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