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Blazing goIITian

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11 Mar 2009 19:42:45 IST

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370

work energy Q frn d c pandey : A block of mass m is attached with a mass less spring of force c

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work energy Q frn d c pandey :A block of mass m is attached with a mass less spring of force constant K. The block is placed over a rough inclined surface for which coefficient of friction u = 3 / 4. Find da ninm value of M reqd to move the block up the plane.

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ramyani chakrabarty

Blazing goIITian

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11 Mar 2009 19:44:52 IST

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ramyani chakrabarty

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11 Mar 2009 19:52:24 IST

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oh , the inclined angle is 37 degree.

ramyani chakrabarty

Blazing goIITian

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11 Mar 2009 19:56:10 IST

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the answer is M = 3 m / 5

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Blazing goIITian

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11 Mar 2009 19:59:52 IST

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M=m(sin 37 + u cos 37) = m (3/5 + 3/5) =6m/5don know wats wrong here:(!

ramyani chakrabarty

Blazing goIITian

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11 Mar 2009 21:18:13 IST

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look block of mass m is attached with a mass less spring of force constant K.

Conjurer

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11 Mar 2009 21:37:38 IST

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The force on the block should be >= gravity and friction

So kx = mg3/5 + 3/4 mg 4/5

For minimum the gain in this PE of the spring should only go to change in PE of mass M.

so Mgx = 1/2 kx^2

2Mg= kx

2Mg = 6mg/5

M = 3mg/5

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Blazing goIITian

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13 Mar 2009 20:56:22 IST

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but wats d fault in mine answer?? will any1 tell?

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Blazing goIITian

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14 Mar 2009 21:05:03 IST

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no reeply??

Madmax

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14 Mar 2009 21:36:07 IST

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See wht the error U are making is tht U consider tht only the mass M is pulling the mass m up the slope, but the fact is tht even the spring conributes to pulling up the block m .This is because of the force constant of the spring which tries to bring a stretched spring back to its original position/condition...... Tht's why U get a answer larger than the actual answer

Conjurer has taken this point into consideration hence has gotten the correct answer.....actually his answer has a typo error.....it is M=3m/5 not M=3mg/5

hope this helps

cheers!!

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