
#1
Jun2611, 09:35 PM

P: 318

1. The problem statement, all variables and given/known data
see it https://docs.google.com/leaf?id=0B5Z...thkey=COG4hNcE sorry for low quality image if you are feeling problem in reading question in image then see this is question Block A is placed on Block B whoose mass greater than that of A. there is a friction between the blocks, while the ground is smooth. A horizontal force P, is increasing linearly with time, begin act on A The acceleration a_{1} a_{2} of A and B respectively are plotted against time choose correct graph. there is a question as well as options. I think all options are incorrect. 2. Relevant equations F=M*a f=u*N 3. The attempt at a solution i think curve should straight line for a little time after a specific time. After a time when upper block slipped from lower one after that time acceleration of upper block is zero(no force) so a_{1} became zero after a time but this is not zero in any figure. 1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution 



#2
Jun2611, 10:08 PM

P: 103

Lets work through some logic because the answer is an option on the work sheet.
So, we know that friction comes in two states: Static Friction and Kinetic Friction. When an object is static, there is a higher coefficient of friction than when an object is sliding on top of another one. You can test this out by applying force to any object on your desk right now. You'll need to apply more force to get it into motion than to keep it in motion. In the terms of our question, this means that since there is no friction under the large box, it will move when very little force is applied to it. And because there is friction between box A and box B, it will take more force to get box A into motion than to keep it in motion. With that in mind, how will the two boxes act when you apply a very light force to box A? 



#3
Jun2611, 10:10 PM

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#4
Jun2711, 12:19 AM

P: 318

what is correct graph 



#5
Jun2711, 01:36 AM

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Well that's strange, graph c is incorrect and graph b is better (and correct if us = uk), but what's that graph you hand sketched in the upper left corner? That one looks even better if us > uk, but also not quite correct for that case.




#6
Jun2711, 02:50 AM

P: 318

If block A does not fall from B but it just slip On block B in that condition what will correct graph. this condition is not in question but i want to know in that case C should most appropriate but slope of a1 should little smaller it's around tan(90) and this is impossible. You say B is better when block A start slipping it's acceleration(a1) will increase with greater rate and in that curve that rate of increase in acceleration is constant 



#7
Jun2711, 03:32 AM

P: 103

I think it's safe to say that this question was poorly planned. It leaves too much room for speculation.
I would say that C is the most correct except for the impossibility of box A suddenly increasing its acceleration into infinity. 



#8
Jun2711, 05:35 AM

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Let's assume that block B is very long so that Block A never falls off it.
Let's focus on the lower block, Block B. After Block A starts slipping, what is the horizontal force acting on Block B (Hint: Draw a Free Body Diagram of Block B). What is the acceleration of Block B at this time? Now a few seconds later, what is the horizontal force acting on Block B, and now what is its accelerataion? None of the given graph's correctly show this. 



#9
Jun2711, 09:50 AM

P: 318





#10
Jun2711, 09:35 PM

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After Block A begins to slip on block B, the force on block B will be constant, so its acceleration will also be constant. Since these are graphs of acceleration vs. time, in my opinion, graph c is far from correct.
I like graph b better, although it should show that the slope of a_{1} increases at the point a_{2} becomes constant. 



#11
Jun2711, 09:43 PM

P: 318




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