QUOTE(bloodchow2 @ Aug 23 2014, 03:59 PM)
1 object on top of wedges is considered inside syllabus, 1 object on top of another object on top of wedges is not in syllabus
there is too many variable for calculating that question, you push lowest object can you guarantee the top 2 will not topple down? how do you so sure the highest object wont fall down? and assumption?
the closest question i have found in entire newton law chapter in University Physics 13th edition is only 2 objects max, which is box on top of wedges, you must be kidding me with 3 objects stack among each other actually in stpm syllabus
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When you say 'wedges', how many are there? 2,3,4?
You could have one million objects on top of another. The internal forces cancel due to Newton's Third Law. The fact that when you treat the upper block and wedge as a single object, you have only 2 objects to consider hits you right in the face when you say that 2 objects are in the syllabus and 3 aren't! This is a completely ridiculous argument!
If you have learnt Newton's Law of Motion well ( I'm starting to doubt that you have ), you will know how and when to treat multiple objects as a single system. This is not unique to any particular syllabus. It's all under Mechanics. In fact, you were taught to model to objects connected by a massless, inextensible rope as a single point particle in Form Four Physics!
In the problem I posted, there are multiple approaches. You can consider each object individually as a single system and the external forces which act on them, or one of them which enables you to find the desired acceleration, or, in
Critical_Fallacy's solution, consider the pseudo-force due to an accelerating reference frame.
As for your comment about the assumptions, I won't touch on that, because it's
trivial from the question that it wants you to find the F in which
the objects don't move relative to each other. So why are you cracking your head about objects toppling and falling?
See, Physics is Physics. I feel sorry when I read your comments about the syllabus difference, what is in the syllabus, what is not, etc. It seems like you've missed the point of education, amidst obsession to swallow what is taught and doing past years aimlessly. You always use external factors as reasons. It's like Tom telling his teacher that his dog ate his homework. Instead of admitting that much has to be learnt ( we all have a lot to learn! ), you emphasise the fact that it's not your fault that you don't know how to solve the problem. You easily put the blame on the fact that 'it's not in the syllabus, so I couldn't care less'.
This post has been edited by maximR: Aug 23 2014, 04:17 PM