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I need help with this question(halliday, resnick and walker, fifth edition, chapter 5 , question 14): PS: I cant draw the figure so I am explaining it as much as possible.

3 wooden blocks are pushed across a frictionless floor.The blocks have masses of 5kg, 2kg and 10kg. The 3 blocks are joined or pressed against each other in the above order. In other words they are moving together.

A force of F acts on the first block i e 5 kg.

The question asks to find the acceleration and force on each block?

I have considered the 3 blocks as 3 different system. Considering motion only in horizontal direction, I would say I got the following equations:

F-f(force on 1st block due to second)=5a1(accn of the 1st block)

f(force on 2nd block due to 1st)-(force on 2nd block due to 3rd)= 2 a2(acc of 2nd block)

f(force on 3rd due to 2nd)= 10 a3

adding all the 3 equations and cancelling the action-reaction forces, I got

F= 5a1+2 a2+10 a3

The question now asks to rank the blocks accroding to their acceleration and the total mass accelerated by 1) F.

I have no clue how to proceed from here. Pls can someone help.

I have seen a similar problem of 2 blocks , and the author assumed common acceleration for both the blocks by considering them as one system

, and then for each block found the net force from free bodied diagram which should be equal to the mass of the individual block*common acceleration.

My question: why is this not the case in the above question? If it were a case it why would the ist question ask to rank the blocks in terms of their acclerations?

I am so confused.

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# Homework Help: -newton's laws

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