KVPY Government Jobs Exams

A nucleus has a half-life of 30 minutes. At 3 PM its decay rate was measured as 120,000 counts/sec. What
will be the decay rate at 5 PM ?
(A) 120,000 counts/sec (B) 60,000 counts/sec
(C) 30,000 counts/sec (D) 7,500 counts/sec

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KVPY Other Question

A point source of light is placed at the bottom of a vessel which is filled with water of refractive index μ to a
height h. If a floating opaque disc has to be placed exactly above it so that the source is invisible from above,
the radius of the disc should be- A book is resting on shelf that is undergoing vertical simple harmonic oscillations with an amplitude of
2.5 cm. What is the minimum frequency of oscillation of the shell for which the book will lose contact with
the shelf ? (Assume that g = 10 m/s2)
(A) 20 Hz (B) 3.18 Hz (C) 125.6 Hz (D) 10 Hz