A boy throws a ball vertically upward with velocity 20 m/s. Time after which ball returns to his hands (g=10) is MCQ with Answer and Explanation

Explanation:
F ∝ m₁m₂. Initial: 1×1 = 1. New masses 2 and 2, product 4, so force = 4F. Distance unchanged. Universal gravitation F = Gm₁m₂/r².

Explanation:
When a body is lifted against gravity, work done (mgh) is stored as gravitational potential energy. This energy can be recovered when the body falls. Kinetic energy relates to motion, thermal to heat, elastic to deformed materials. The conservation of energy principle states that work done against conservative forces becomes potential energy. Formula: PE = mgh, where h is height above reference. Memory aid: 'Potential' means stored energy due to position. This conceptual question tests energy transformation understanding, frequently appearing in work-energy theorem applications in competitive exams.

Explanation:
An ideal solenoid consists of tightly packed coils. When current passes through it, the magnetic field lines inside the solenoid are parallel straight lines. This indicates that the magnetic field is uniform in magnitude and direction at all points strictly inside the central region of the solenoid. The field strength is given by B = mu_0 * n * I.