1anyone trying out ???
spring const. = k
all surfaces are smooth.
u hav to find out the elongation in the spring.
I have brought out 2 solutions....tell me which one is right.
Soln. A :
kx = mg sinθ
x= mg sinθk
Soln. B :
Consider the extension as x along the plane.
Hence initial height of the block from the final position is x sinθ.
Conserve energy :
mgx sinθ = 12kx2
Hence x = 2mg sinθk
which is the answer given in the book.
Although i've done the 2 solns. myself......i find no violation of laws with soln. A. And Soln. B is also perfectly correct. Then where is the contradiction ???
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12 Answers
3dude i think u need to find the maximum extension rite.
In soln A u r rong since at the maximum extension aceleration=-w2x
In soln B i think its correct since u have conserved energy at initial and final states.
i will say dat first think for some more minutes,i am sure u can find which one is rong.
19this is a very commonly made mistake...we are confusing equilibrium with "rest" !
to apply the first method we need to ensure the position where the acceleration of the body is zero,not its velocity ! in fact, acceleration and velocity,in this case and also in other cases(like shm of pendulum) , are zero at different points of time !
1okie understood ....thnx.........................@.msp : any diff. soln. ?
24ya organic has given a perfect reply...
mgsinθ=kx doesnt guarantee rest..it just guarantees uniform velocity...
whereas energy conservation guarantees rest to rest situation
1am I the only one to notice "ALL surfaces are smooth" ?
even the book seems to have ignored it .. unless of course its a typo or something and not the book's fault
24i dont think wedge is moving...........it is fixed...
whenver wedge is moving its normally given clearly..