QUES: Matter may be converted to energy (and vice versa), but mass cannot ever be destroyed; rather, mass/energy equivalence remains a constant for both the matter and the energy, during any process when they are converted into each other. However, since  is extremely large relative to ordinary human scales, the conversion of ordinary amount of matter (for example, 1 kg) to other forms of energy (such as heat, light, and other radiation) can liberate tremendous amounts of energy (~ joules = 21 megatons of TNT), as can be seen in nuclear reactors and nuclear weapons. Conversely, the mass equivalent of a unit of energy is minuscule, which is why a loss of energy (loss of mass) from most systems is difficult to measure by weight, unless the energy loss is very large. Examples of energy transformation into matter (i.e., kinetic energy into particles with rest mass) are found in high-energy nuclear physics.

Why is a gain of energy difficult to measure by weight?
What is the answer?
ANS: unanswerable
QUES: A freight elevator, or goods lift, is an elevator designed to carry goods, rather than passengers. Freight elevators are generally required to display a written notice in the car that the use by passengers is prohibited (though not necessarily illegal), though certain freight elevators allow dual use through the use of an inconspicuous riser. In order for an elevator to be legal to carry passengers in some jurisdictions it must have a solid inner door. Freight elevators are typically larger and capable of carrying heavier loads than a passenger elevator, generally from 2,300 to 4,500 kg. Freight elevators may have manually operated doors, and often have rugged interior finishes to prevent damage while loading and unloading. Although hydraulic freight elevators exist, electric elevators are more energy efficient for the work of freight lifting.[citation needed]

How do freight elevators differ from passenger elevators?
What is the answer?
ANS: Freight elevators are typically larger and capable of carrying heavier loads than a passenger elevator
QUES: On 28 January 1871 the Government of National Defence based in Paris negotiated an armistice with the Prussians. With Paris starving, and Gambetta's provincial armies reeling from one disaster after another, French foreign minister Favre went to Versailles on 24 January to discuss peace terms with Bismarck. Bismarck agreed to end the siege and allow food convoys to immediately enter Paris (including trains carrying millions of German army rations), on condition that the Government of National Defence surrender several key fortresses outside Paris to the Prussians. Without the forts, the French Army would no longer be able to defend Paris.

On what date did the Government of National Defence negotiate an armistice?
What is the answer?
ANS:
28 January 1871