Answer: object B is negatively charged, object C is positively charged and object D is also positively charged
Explanation: since unlike charges attract and like charges repel, for object A which is positively charged and B to attract B must be negatively charged and then for B which is negatively charged and C to attract C must be positively charged and for C and D to repel they have to be of thesame charge which means D is positive as well.
If you take a fluid (i.e. air or water) and heat it, the portion that is heated usually expands. The same mass takes up more volume and as a consequence the heated portion becomes less dense than the portion that is<span><span> not heated.</span> </span>
I didn’t know water has calories
The heat coming from the sun warms the land more quickly than the sea. As a result of these, the air near the land warm up and rises and the cooler air from the sea moves in to replace the risen air. The correct answer is option A
There will be heat transfer from a region of higher temperature to the region of lower temperature. But in the case of land and sea breeze, the transfer of heat are the result of convectional current in nature. Because the land is a better absorber of heat and also has a lower specific heat capacity compare to sea, during the day, the heat coming from the sun warms the land more quickly than the sea. As a result of these, the air near the land warm up and rises.
The cooler air from the sea moves in to replace the risen air.
Why do ocean winds or sea breezes blow toward shore during the day ? It is because air over the beach heats up, rises and is replaced by ocean air.
Therefore, option A is correct
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The elastic potential energy of a spring is given by

where k is the spring's constant and x is the displacement with respect to the relaxed position of the spring.
The work done by the spring is the negative of the potential energy difference between the final and initial condition of the spring:

In our problem, initially the spring is uncompressed, so

. Therefore, the work done by the spring when it is compressed until

is

And this value is actually negative, because the box is responsible for the spring's compression, so the work is done by the box.