Energy principle example problem in classical mechanics book

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SUMMARY

The discussion focuses on a physics problem from the book "Classical Mechanics" by R. Douglas Gregory, where a man of mass 100 kg pulls a block of mass 1600 kg using a force that is two-fifths of his weight. The maximum force he can exert is calculated to be 400 N, contradicting a stated force of 200 N in the solution. Participants confirm that the correct force should indeed be 400 N, emphasizing the importance of accurate calculations in applying the Work-Energy principle.

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certainice
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Homework Statement


A man of mass 100 kg can pull on a rope with a maximum force equal to two fifths of his own weight. [Take g = 10 ms^2] In a competition, he must pull a block of mass 1600 kg across a smooth horizontal floor, the block being initially at rest. He is able to apply his maximum force horizontally for 12 seconds before falling exhausted. Find the total work done by the man and confirm that the energy principle is true in this case.

Homework Equations


F*v*dt=W , Work-Energy principle

The Attempt at a Solution



0http://physics.stackexchange.com/questions/279513/energy-principle-example-problem-in-mechanics-book# The problem as stated in the book Classical Mechanics by R Douglas Gregoryhttps://books.google.co.uk/books?id...equal to two fifths of his own weight"&f=false .I only have an issue with a portion of the problem.Part of the solution to that example problem states that the force he applies is a constant 200 N. But shouldn't it be 400 N since the problem states that he pulls with a maximum force of two-fifths of his own weight and his weight is 1000 N and two-fifths *1000 is 400 N? Maybe I am missing something here.
 
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Hi certainice, Welcome to Physics Forums!

It's not unheard of for there to be typos in textbooks, particularly if example problems are "updated" for new editions. 2/5 of 1000 is indeed 400, not 200.

Do the derivation yourself symbolically rather than plugging in numbers, or just show that your own numerical results demonstrate the principle being examined.