hello everyone
Could Some one Please help me with this homework the question is :


The mythical wizard Merlin had driven the sword Excalibur through a stone or anvil. It was said that only the true future ruler could pull it out. After numerous renowned knights and nobles failed at this task, Arthur, the son of the English Great King Uther Pendragon, managed to effortlessly free the sword, making him the rightful king.

Like you, I also doubt that Merlin was truly a wizard. Perhaps he was a clever electrical engineer like you and came up with the following idea. He prepared the sword by isolating the tip from the rest of the blade and charging it with a positive charge = 12 μC. Then, he inserted the sword into a basalt stone with ε = 2.5. At a distance of ℎ = 10 , he positioned a negative, ring-shaped line charge with a radius = 20 . He sized this charge so that the resulting force on the charge at the sword's tip was so great that no one could pull the sword from the stone.

Now, he just had to wait for Arthur's turn. Quickly discharging the line charge, Arthur could easily pull the sword from the stone without any problems.

Task: Show that you are just as clever as Merlin. How large must the line charge density be so that a person with a pulling force of = 1 kN is unable to pull the sword from the stone?

 

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