I do not need help solving the problem. I am having a problem understanding why
ID: 1584328 • Letter: I
Question
I do not need help solving the problem. I am having a problem understanding why in the first diagram if F cos 30 is pointing to the left why is it positive F cos 30 and not negative F cos 30? In the second diagram F cos 37 is pointed to the right why is negative Fd cos theta and not positive Fd cos theta? Does it have to do with the way the applied force is pointed? The applied force is pointed away from the block, is this the reason F cos 30 is positive in the first diagram? In the second diagram the applied force is pointed towards the block, is this the reason F cos 37 negative? Please answer the above question and not just given the answer. Having problems understanding this concept. Thank you
A 4.0-kg block is lowered down a 37° incline a If F 40 N and M-2.0 kg, what is the magnitude of the acceleration of the suspended distance of 5.0 m from point A to point B. A object? All surfaces are frictionless. horizontal force (F 10 N) is applied to the block between A and B as shown in the figure. The kinetic energy of the block at A is 10 J and at B it is 20 J. How much work is done on the block by the force of friction between A and B? F sin 30 F cos mg 4.0 kg AM Initial kinetic 10J F sin 37 5.0 Fcos 37 mg 37 -1 0 J > final kinetic mg For 2M F cos 30 TE 2ma energy Wnetke - ke, PE+f+ F- ke, - ke, | mgd + f-Fd cos -ke-ke, For M T-mg ma F cos 30-T + T-mg = 2ma + maExplanation / Answer
The problem arises because the force is a vector quantity, and in free body diagrams like these, we resolve the components of the forces, and equate them.
As far as signs (positive or negative ) are concerned, here is a key rule to avoid confusion:
For a given free body diagram of any body, consider the components of forces acting along the direction of motion (and hence, the direction of net acceleration of the body 'a') as positive. Whereas, the components opposite to the direction of motion are taken as negative.
Following this sign convention, one can easily balance the components.
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