575 - Physics Questions Answers

A bomb of mass M @ rest explodes into 2 fragments of masses m1 &m2 . The total energy released in the explosn is E if E1 &E2 represent the energies carried by m1 &m2. then which of the followg is correct

a) E1=(m2/M)E

B) E1= m1/m2  E

C) E1= m1/M  E

D) E1= m2/m1  E

Asked By: SARIKA SHARMA
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Joshi sir comment

(1) is correct 

the ratio of energy will be E1/E2 = m2/m1

A block of mass m takes t to slide down on a smooth inclined plane of angle of inclination and height h. If same block slids down on a rough inclined plane of same angle of inclination and some height and takes time n times of initial value, then coefficient friction between block and inclined plane is

the answer is [1- 1/n² ] tanθ

Asked By: AVANTIKA PURI
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Joshi sir comment

in first case acceleration is gsinθ

and in second case acceleration is gsinθ-μgcosθ

now use s = 1/2 a tin both the case and solve 

A block of mass m is at rest on a rough inclined plane of angle of inclination θ . If coefficient of friction between the block and the inclined plane is required to move the block on the plane is

how the answer is   mg[sinθ - μ cosθ]  .

 

Asked By: AVANTIKA PURI Solved By: SARIKA SHARMA
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Joshi sir comment

i think one line is missing in the question.

 a point charge q is placed at a distance 2r from the centre O of a conducting charged sphere of radius r. due to induced charges on the sphere , find the elecric potential at point P on the surface of sphere in volt if kq/r =18V.

 in the above ques, last time u found out potential at center but according to ques we hav eto find out on the surface and ans. is 3 

Asked By: VISHAL PHOGAT
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Joshi sir comment

if the answer is 3 V then 2r should be the distance of q from surface not from centre.

first confirm

In the ques previously submitted by someone which was as follow

the electric field vector is given by E= a(x)1/2 i^ . find the φ thru a cube bounded by surface x=l, x=2l, y=0, y=l , z=l, z=0.

Sir , my query is that in the solutn submitted the leaving flux at x=2l is given as( 2l)1/2 X l2 . but as the electric field is itself along x then why 2l will be used as along x axis it will be zero because cosθ used is perpendicular to surface with electric field axis thus cos90 =0??

Asked By: SARIKA SHARMA
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Joshi sir comment

θ should be measured between E and perpendicular drawn on the surface

a small body starts sliding from a height h down an inclined groove passing into a half circle of radius h/2. find the speed of the bodywhen it reaches the highest point of its trajectory

Asked By: DANI
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Solution by Joshi sir

since body starts from height h at rest and ends in the same height so it will again be in rest 

BLOCK OF WOOD IS KEPT ON THE FLOOR OF A STATIONARY ELEVATOR. D ELEVATOR BEGINS TO DESCEND WITH AN ACCLN 12m/s2 . IF g =10  , THEN DISPLACEMENT OF BLOCK W.R.T. GROUND DURING FIRST 0.2 SEC. AFTER D START WILL BE             ??

ANS 0.2m

Asked By: SARIKA SHARMA
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Joshi sir comment

s = ut + 1/2 at2

so s = 0 + 1/2 10(0.2)2

so s = 5(0.04) = 0.2

since elevator is moving with an acc. greater than g so we should take it a free fall

4 particles each of mass m and charge q are held at the corners of a square of side a . they are released  at t=0 and move under mutual repulsice force. find the speed of any particle when its distance from the center is double.

Asked By: VISHAL PHOGAT
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Joshi sir comment

potential energy in initial condition = 4*k*q*q/a + 2*k*q*q/a√2

potential energy in final condition = 4*k*q*q/2a + 2*k*q*q/2a√2

and kinetic energy in the final condition = 4*mv2/2

now use energy conservation

a point charge q is placed at a distance 2r from the centre O of a conducting charged sphere of radius r. due to induced charges on the sphere , find the elecric potential at point P on the surface of sphere in volt if kq/r =18V.

Asked By: VISHAL PHOGAT
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Joshi sir comment

potential at the centre due to q = kq/2r = 9 V

potential at centre due to surface charge = 0 V

total potential = 9 V

now at surface potential due to q = kq/r = 18 V

but it should be 9 V totally so due to surface induction, potential will be -9V

the electric field vector is given by E=a(x)½ iˆ.find the flux through a cube bounded by surfaces x=l ,x=2l, y=0 ,y=l, z=0, z=l

Asked By: VISHAL PHOGAT
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Joshi sir comment

entering flux at x=l will be a(l)1/2  *  l2

leaving flux at x=2l will be a(2l)1/2  *  l2

so net flux will be the difference of these 2 flux

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