A ball is dropped from a height of 20 m. Time to reach ground (g=10) is MCQ with Answer and Explanation

Explanation:
First, convert speed to SI units: 72 km/h = 72 × (5/18) m/s = 20 m/s. Initial velocity (u) = 0, final velocity (v) = 20 m/s, time (t) = 10 s. Acceleration (a) = (v-u)/t = 20/10 = 2 m/s². Distance (s) = ut + (1/2)at² = 0 + 0.5 × 2 × 10² = 100 meters.

Explanation:
Silicon semiconductor, abundant, efficient for photovoltaic cells. Also gallium arsenide. Solar cells convert light to electricity. Renewable energy technology.

Explanation:
Number of half-lives = 30/10 = 3. Remaining = (1/2)³ = 1/8. Exponential decay N = N₀(1/2)^(t/T). Radioactive decay constant λ = ln2/T.