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# At a construction site, a 65.0-kg bucket of concrete hangs ISBN: 9780321675460 31

## Solution for problem 41P Chapter 7

University Physics | 13th Edition

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Problem 41P

At a construction site, a 65.0-kg bucket of concrete hangs from a light (but strong) cable that passes over a light, friction-free pulley and is connected to an 80.0-kg box on a horizontal roof (Fig. P7.37). The cable pulls horizontally on the box, and a 50.0-kg bag of gravel rests on top of the box. The coefficients of friction between the box and roof are shown. (a) Find the friction force on the bag of gravel and on the box. (b) Suddenly a worker picks up the bag of gravel. Use energy conservation to find the speed of the bucket after it has descended 2.00 m from rest. (Use Newton’s laws to check your answer.)

Step-by-Step Solution:

Solution to 41P Step 1 Mass of the bucket =65kg Mass of the block =80 kg Mass of the bag of gravel =50kg k0.400 s0.700 Step 2 Frictional force between block and bag of gravel F f Since the block is in state of rest, static friction exists for bag of gravel and the block. Frictional force on the bag of gravel =F fg F = mg=0.7x50x9.8 fg s F =343N fg Frictional force between block and the horizontal surface=F fb Ffb s=0.7x80x9.8 Ffb48.8N (a) Total frictional force between the horizontal surface and the block and bag system =F f Ff fg fb Ff43+548.8 Ff891.8N

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##### ISBN: 9780321675460

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