Which scientist is associated with the theory of relativity? MCQ with Answer and Explanation

Explanation:
A lactometer is a specific type of hydrometer used to test the purity of milk by measuring its relative density. All hydrometers, including lactometers, work on Archimedes' Principle of buoyancy. They float at a depth that depends directly on the density of the liquid; they sink deeper in less dense liquids (like milk heavily diluted with water).

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.

Explanation:
Fuse is a safety device: thin wire melts when current exceeds safe limit due to short circuit or overload, breaking circuit. Prevents fire and appliance damage. Based on heating effect. MCB is modern alternative.