Suppose you had two small boxes, each containing 1.0 g of protons. (a) If one were placed on the moon by an astronaut and the other were left on the earth, and if they were connected by a very light (and very long!) string, what would be the tension in the string? Express your answer in newtons and pounds. Do you need to take into account the gravitational forces of the earth and moon on the protons? Why? (b) What gravitational force would each box of protons exert on the other box?

Question

Suppose you had two small boxes, each containing 1.0 g of protons. (a) If one were placed on the moon by an astronaut and the other were left on the earth, and if they were connected by a very light (and very long!) string, what would be the tension in the string?  Express your answer in newtons and pounds.  Do you need to take into account the gravitational forces of the earth and moon on the protons? Why? (b) What gravitational force would each box of protons exert on the other box?

drwls · Answer

Calculate the number of protons that have a mass of 1 g. (Get that by dividing 1 by the number of grams per proton). Then calculate the charge of that amount of protons by multiplying by the proton charge.

Charge = 1 g * (1.602*10^-19C)/(1.672*10^-24 g)= 9.58*10^4 C

Use Coulomb's law to get the repulsion force when they are separated by the earth-moon distance.

For the weight force exerted by the earth and moon, use Newton's law of gravity or just multiply the total proton mass by g (for the earth) or g/6 (for the moon). I susepect they will be nelgligible compared to the electrospatic force. The same goes for the gravity force of the boxes on each other.

Do these calculations yourself; it will be a useful exercise for you.

acegsm · Answer

Would that end up being 0.0065 N?

a · Answer

no

Anonymous · Answer

its 560 N for you guys that could not figure it out (like me)