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titansarus

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## Homework Statement

Question from fundamental of physics, Halliday Resnick Walker

In Figure below, a ##m=0.250## kg block of cheese lies on the floor of a ##M=900 kg## elevator cab that is being pulled upward by a cable through distance ##d1 =2.40 m## and then through distance ##d2 = 10.5 m##. (a) Through d1, if the normal force on the block from the floor has constant magnitude ##F_N## = 3.00 N, how much work is done on the cab by the force from the cable? (b) Through d2,if the work done on the cab by the (constant) force from the cable is 92.61 kJ, what is the magnitude of ##F_N##?

## Homework Equations

##W = F d## (in 1 dimension)

##\Sigma F = m a##

##\vec F_{12} = - \vec F_{21}##

3. The Attempt at a Solution

3. The Attempt at a Solution

I don't have problem at the solution itself, My problem is with the solution of the book.

Answer of the book:

**##F_N## and its reaction (Newton 3rd Law) cancel each other**. (i.e. they are Internal Forces for the system). Also for the second part, I think we must find F with ##W = F d## and then find ##a## using (##**## equation) and then find ##F_N## with (##*## equation). Is my solution correct?