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![[Post New]](/templates/default/images/icon_minipost_new.gif) 28 Mar 2008 01:18:48 IST
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Today, I was casually looking through the "Friction" section of the book when this caught my attention. Check out Prob 6.1 in Page.85 (Chap- Friction).
In the (b) section, when finding the magnitude of contact force, it is done using pythagorus theorem concepts. But, isn't it meant to be done with parallelogram law of vector addition ?
This is challenging my whole conception of the concepts. Pls help me. 
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28 Mar 2008 01:23:05 IST
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it is clearly given dude...the angle between N anf f is 90deg...so using pytho or parallelo rule is the same as in this case pytho is a corolary of the paralelogram law of vectors coz cos90 is zero...
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always remember to chill if im wrong..though it generally doesnt happen.
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28 Mar 2008 01:25:15 IST
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actually f and N are always perpendicular
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always remember to chill if im wrong..though it generally doesnt happen.
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28 Mar 2008 01:31:05 IST
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I don't understand man. Using Parallelogram law, we'll end up with 7N while with Pythogorus, with 5N. Pls explain your point.
For those who want the question :
Example.6.1: A body of mass 400g slides on a rough horizontal surface. If the frictional force is 3N, find
(a) Angle made by the contact force with the vertical.
(b) Magnitude of the contact force.
I've doubt regarding (b). :(
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28 Mar 2008 01:32:41 IST
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just see the para right before the example 6.1
ul understand better
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always remember to chill if im wrong..though it generally doesnt happen.
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28 Mar 2008 01:36:25 IST
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I read it. It just says that normal force and frictional force are perpendicular. Honestly, I can't still understand the stuff going on. :(
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28 Mar 2008 01:40:51 IST
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i donno....but from that para u have to get 5N because theres no cos term there...so the only vectors acting there are the friction and the normal reaction...they are always perpendicular so their resultant is given by sqareroot of(N2+f2+2f.N) as f.N=0 we get the required answer
hope its clear...
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hey..they have to be perpendicular to each other because they are the components afterall and the contact force F is not perpendicular to the surface so it is resolved along the ground n perp to the ground...so these two perpendicular components emerge...using this fact..the dude(hc verma) made up a problem so that u get the original vector if u know the components..the indirect way...
hope uv understood..
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always remember to chill if im wrong..though it generally doesnt happen.
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28 Mar 2008 13:05:55 IST
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Yeah. I've understood man. I was a little cranky I almost forgot these basics. Thanks man.
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