IIT-JEE Exam

Three concentric metallic spherical shells of radii R, 2R, 3R, are given charges Q1, Q2, Q3, respectively. It
is found that the surface charge densities on the outer surfaces of the shells are equal. Then, the ratio of the
charges given to the shells, Q1 : Q2 : Q3, is
(A) 1 : 2 : 3 (B) 1 : 3 : 5
(C) 1 : 4 : 9 (D) 1 : 8 : 18

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IIT-JEE Other Question

Two small particles of equal masses start moving in opposite directions from a point
A in a horizontal circular orbit. Their tangential velocities are v and 2v respectively,
as shown in the figure. Between collisions, the particles move with constant speeds.
After making how many elastic collisions, other than that at A, these two particles
will again reach the point A?
(A) 4 (B) 3
(C) 2 (D) 1 A ball is dropped from a height of 20 m above the surface of water in a lake. The refractive index of water
is 4/3. A fish inside the lake, in the line of fall of the ball, is looking at the ball. At an instant, when the ball
is 12.8 m above the water surface, the fish sees the speed of ball as
(A) 9 m/s (B) 12 m/s
(C) 16 m/s (D) 21.33 m/s