IIT-JEE Exam

A uniformly charged thin spherical shell of radius R carries uniform
surface charge density of σ per unit area. It is made of two hemispherical
shells, held together by pressing them with force F..F is
proportional to

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IIT-JEE Other Question

A block of mass 2 kg is free to move along the x–axis. It is at rest and from t =
0 onwards it is subjected to a time–dependent force F(t) in the x direction. The
force F(t) varies with t as shown in the figure. The kinetic energy of the block
after 4.5 seconds is
(A) 4.50 J (B) 7.50 J
(C) 5.06 J (D) 14.06 J. A tiny spherical oil drop carrying a net charge q is balanced in still air with a vertical uniform electric field
of strength 81pie/7* 10^5Vm^–1. When the field is switched off, the drop is observed to fall with terminal
velocity 2 × 10^–3 ms^–1. Given g = 9.8 ms^–2, viscosity of the air = 1.8 × 10^–5 Ns m^–2 and the density of oil =
900 kg m^–3, the magnitude of q is