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atomic structure

by Astitwa Lathe -

The ionisation energy of Hydrogen-atom is 13.6 ev.H-atoms in the ground state are excited by monchromatic light of energy 12.1 ev.The spectral lines emitted by H-atoms according to Bohr's theory will be:

(A)n=3 to n=1 (B) n=3 to n=2 (C) n=2 to n=1 (D) n=4 to n=1 

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Mechanics Problem

by Rahul Sharma -
All the surfaces shown in figure are assumed to be frictionless. The block of mass m slides on the prism of mass M which in turn slides backward on the horizontal surface. Find the acceleration of the smaller block with respect to the prism.
 
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Well I found out acceleration of both the blocks and then considered a pseudo force on the smaller block since we have to find acceleration with respect to the accelerating prism. I got two accelerations acting on smaller block m making an angle theta and then I took resultant of the two accelerations but ended up with the wrong answer, someone please help!
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conic section

by lokesh sardana -

If foci of the ellipse x2/a2 + y2/b2 = 1  and hyperbola x2/144 - y2/81=1/25,then the value of b2 is...<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

a) 1

b) 5

c) 7

d) 9

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Trigonometery

by Chandni Bhatia -
The equation kcosx-3sinx=k+1 is solvable only if k belongs to the interval [A][4,INFINITY] [B] [-4,4] [C] (-INFINITY,4] [D] NONE OF THESE.
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Friction

by Chandni Bhatia -

Let F,FN AND f denote the magnitudes  of the contact force,normal force and the friction exerted by one surface on the other in contact.If none of these is zero,A)F>FN B)F>f C)FN>f D)FN-f<F<FN+f.Contact force has to be smaller than frictional and normal force .My dobt is in option d.

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Centre of mass

by Chandni Bhatia -

In which of the following cases the centre of mass of a rod is certainly not at it's centre?

(A) The density continuously increases from left to right.(B)The density continuously decreases from left to right .(C)The density decreases fron left to right upto the centre and then increases. (D) The density increases from left to right upto the centre and then decreases.

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conic section

by lokesh sardana -

The locus of the point of the cord of contact of tangents from which to the ellipse x2/a2 + y2/b2 = 1 touches the circle x2+y2=c2 is__________

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