Static Electricity Legacy Problem #5 Guided Solution

A successful solution to a physics problem involves reading the problem carefully and identifying the known quantities and the unknown quantities, and then planning a strategy to get from known to unknown. Now as we identify those known and unknown quantities, it is preferred that you begin to write that information down. And as you do, give specific attention to the units that are on the stated quantities. Here in this problem, we are to calculate the amount of force of attraction between two students who develop one coulomb of charge. The positive and the negative one coulomb of charge stated in this problem are simply the sign of the charge, or the type of the charge, plus versus minus. When I do my calculation of the amount of force of attraction, I'm going to tend to ignore this plus and the minus, because including the plus and minus sign in my actual calculation does not reveal any informative information that I didn't already know. Now I also know the distance between Tyrone and Meara. In part A of the problem, they're one meter apart. In part B of the problem, they're 52 kilometers apart, and there I give attention to units. And in part C of the problem, they're 1,900 kilometers apart. Now the significance of that unit meter versus kilometers is as I go to substitute numbers into my coulombs law equation, I need to take into consideration that the value of k has in it units of meters squared. And so when I substitute one meter, 52 kilometers, and 1,900 kilometers distances into that coulombs law equation, I have to make sure I substitute them in such a way that my units of meters cancels when I do my calculation. Now the value of k is 8.99 times 10 to the ninth newtons times meters squared per coulombs squared. So substituting in 1.0 coulombs for my value of q1 and q2 respectively, and then substituting in the distances that are given in units of meters will give me newtons as the unit of my answer. So in part B and part C, where I have kilometers as my unit of distance, I need to use the fact that there are 1,000 meters in one kilometer in order to convert that kilometer distance to units of meters. I need to give good thought there if the distance is 52 kilometers and I ask, how many meters is that equivalent to? It would be absurd if I were to describe 52 kilometers as being equivalent to 0.052 meters. 0.052 meters is hardly even a twentieth of a meter stick. And so I need to do proper conversions, moving the decimal place three places to the right. Doing the careful mathematics will get you the answer. Good luck to you.