A man of mass 60 kg stands on a weighing machine in a lift accelerating upward at 2 m/s². Reading in kg wt (g=10) is MCQ with Answer and Explanation

Explanation:
Equilibrium occurs where the net force is zero, meaning dU/dx = 0. Given U(x) = ax^2 - bx, taking the derivative: dU/dx = 2ax - b = 0. Therefore, x = b / 2a. To confirm it's stable, the second derivative d^2U/dx^2 must be positive. d^2U/dx^2 = 2a. Assuming 'a' is positive, it represents a stable equilibrium point.

Explanation:
This is based on the conservation of angular momentum (L = Iω), where 'I' is the moment of inertia and 'ω' is angular velocity. When the boy extends his arms, mass moves further from the axis of rotation, increasing his moment of inertia (I). Since 'L' is conserved, an increase in 'I' must result in a decrease in angular velocity (ω).

Explanation:
Superconductivity occurs in certain materials below a critical temperature T_c, where electrical resistance drops abruptly to zero, and magnetic fields are expelled (Meissner effect). Option B describes insulators; C and D are unrelated. Memory aid: 'Superconductor: R=0 below T_c; perfect diamagnetism'. This modern physics concept is frequently tested in competitive exams. Always distinguish superconductivity (zero resistance) from perfect conductivity (theoretical limit); real superconductors exhibit Meissner effect, a defining property.