Which gas is filled in an electric bulb? MCQ with Answer and Explanation

Explanation:
g = GM/R² = G (ρ 4/3 π R³)/R² ∝ ρ R. If radius half, density same, g becomes half. Weight half = 50 N.

Explanation:
Leading zeros (before first non-zero digit) are not significant. So 0.0034060: the first non-zero is 3, then 4,0,6 are significant, and the trailing zero after decimal is significant. Thus significant digits are 3,4,0,6,0 — 5 digits. Note: The last zero indicates precision. Answer is 5.

Explanation:
By conservation of momentum: initial momentum = 0 (system at rest). Final momentum: m_bullet×v_bullet + m_gun×v_gun = 0. Thus (0.02 kg)(300 m/s) + (2 kg)(v_gun) = 0 ⇒ 6 + 2v_gun = 0 ⇒ v_gun = -3 m/s. Magnitude is 3 m/s; negative sign indicates opposite direction to bullet. This demonstrates momentum conservation in isolated systems. Memory tip: Recoil velocity = -(m_bullet/m_gun)×v_bullet. Such numerical problems test application of conservation laws, frequently appearing in competitive exams with varying mass ratios and velocities.