Comparison of electric & gravity forces: Two identical blocks are placed 5 m apa

Question

Comparison of electric & gravity forces: Two identical blocks are placed 5 m apart. Each has a mass of 3 kg, is electrically neutral, and is made entirely of copper. Note: One copper atom has a mass of 1.055x10^-25 kg and contains 29 protons. How many electrons must a neutral copper atom have? 29 electrons Estimate the percentage of a copper atom's mass that is due to: electrons: 025 protons: 45.99 Do a proton & electron have an equal amount of charge? Of mass? Also, what constitutes the remaining mass of these copper atoms? Estimate how many electrons each of these blocks has within it. 8.24e26 electrons What is the total charge of all these electrons? -1.32e8 C And what is the total charge of all the protons in a block? 1.32e8 C So what is the net charge of each block? 0 c You now remove an equal amount of electrons from each block, so the electric repulsion of the blocks cancels their gravitational attraction to each other. (Note: You may assume the mass of the blocks is not significantly reduced when removing these electrons- why?) What is the net charge of each block now? -2.58e-10 C How many electrons were removed from each block? Give a number, and then also express this as a percentage of the total number in the block. 1.61e9 electrons removed 1.95e-16 % Did your answers for this part depend on the distance between the blocks? Suppose ALL of the electrons suddenly disappeared from the blocks. How much repulsive force would the blocks exert on each other (initially, before each block itself dispersed)? Express in Newtons and as multiples of the weight of a jetliner (about 106 N). 6.27e24 N 6.27e18 times the weight of a jetliner Final thought: What did you discover about the relative strengths of the gravity force vs. the electric force?

Explanation / Answer

The mistake u made is

since we are removing electrons the net charge will be positive you took it negative hence got wrong answer

given that we have to balance electric repulsion with gravitational force

k*q1*q2/r^2 = G*M1*M2/r^2

q1=q2 and M1=M2 =3kg , k=9*10^9 ,G = 6.67*10^-11

hence qe have

q1^2 = G*M1*M2 /k = 6.67*10^-20

hence q1 = +2.58*10^-10 Columb

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