The half-life of a radioactive element is 5 days. After 20 days, the fraction undecayed is MCQ with Answer and Explanation

Explanation:
Heat travels through spoon from hot end to cold end by conduction (molecular vibration and free electrons). Handle gets hot. Metal good conductor.

Explanation:
Maximum friction = μN = 0.4×50 = 20 N. Weight = 50 N. Friction < weight, so block will fall. Wait, force 50 N horizontal, weight 5×10=50 N. Frictional force upward max 20 N, weight 50 N down, net downward 30 N, so it slides down. So it falls down. Answer A. Let's correct: option A: Falls down. I'll set A.

Explanation:
Ionosphere contains ions and free electrons, reflects radio waves back to Earth, enabling long-distance radio communication. Used in skywave propagation. Troposphere weather layer.