Answer:
Let the mass of the book be "m", acceleration due to gravity be "g", velocity be "v" and height be "h".
Now if we are holding a book at a certain height (h), <em><u>the potential energy will be maximum which is equal to mass× acceleration due to gravity× height (= mgh)</u>.</em>
(Remember: kinetic energy =0)
Now we consider that the book is dropped, in this case a force will act downward towards the centre of the earth, <em><u>Force= mass× acceleration due to gravity (F=mg)</u></em>. It is equal to the weight of the book.
While the book is falling, the potential energy stored in the book converts into kinetic energy and strikes the floor with <em><u>the maximum kinetic energy= (1/2)×mass×velocity² (=1/2mv²)</u>.</em>
(Remember: kinetic energy=0)
Due to this process the whole energy is conserved.
As the potential energy decreases kinetic energy increases.
Work = Force * distance
Force = 70 N
Work = 3500 J
3500 = 70d
d = 3500/70 = 50 m
Photovoltaic cells are the most efficient means of converting solar energy to electricity. Option b is correct.
<h3>What is a cell?</h3>
A cell is a voltage and current-producing device that consists of a single anode and cathode separated by an electrolyte.
One or more cells can make up a battery. One cell, for example, is one AA battery.
Light intensity on a solar cell is often measured in "suns," with one sun roughly equivalent to 1 kW/m².
Concentrated sunlight improves the ratio of current generated while the device is lighted vs when it is dark, hence enhancing output voltage and efficiency.
Photovoltaic cells are the most efficient means of converting solar energy to electricity.
Hence, option b is correct.
To learn more about the cell refer to:
brainly.com/question/3142913
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Is that a question? .
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(a). If the temperature of a substance is increased the density of it will also increased. The temperature is directly proportional to the density because the molecular activity of the substance will be affected by the temperature
(b).The mass of the substance doesn't at all. Because the amount of matter inside the substance cannot be affected by the temperature except that its water