A radioactive substance decays to 1/16th of its original mass in 20 days. Half-life is MCQ with Answer and Explanation

Explanation:
Moderator (water, graphite) slows fast neutrons to thermal energies for efficient fission in U-235. Control rods absorb neutrons to regulate reaction. Memory tip: 'Moderator = neutron slower; Control rods = neutron absorber'. Reactor component function frequently tested in competitive nuclear physics questions.

Explanation:
p = m v = 5 × 2 = 10 kg m/s. Direction same as velocity. Momentum vector. Unit kg·m/s.

Explanation:
Seven base units: metre, kilogram, second, ampere, kelvin, mole, candela. All other units derived. This is standard definition. Supplementary units radian and steradian now considered dimensionless derived units.