Physics A: Problem Set 2: Electrosatic force

practice

1. Given three charges in a standard coordinate system…
   1. +10 μC at (+0 m, +0 m)
   2. −40 μC at (+0 m, +9 m)
   3. +20 μC at (−3 m, +0 m)

   Calculate the magnitude and direction of the net electrostatic force on the first charge. Solve this problem in stages.

   1. Sketch the arrangement of the charges.
   2. Calculate the magnitude of the force of charge 2 on charge 1.
   3. In what direction does the force you just calculated point?
   4. Calculate the magnitude of the force of charge 3 on charge 1.
   5. In what direction does the force you just calculated point?
   6. What is the magnitude of the resultant of the two forces you just calculated?
   7. What is the direction of the resultant of the two forces you just calculated relative to the +x axis?

homework

2. Compare the magnitude of the electrostatic and gravitational forces between…
   1. an electron and proton in a hydrogen atom (the radius of the electron's orbit is about 0.053 nm)
   2. two protons in a helium nucleus (the separation between them is about 1.2 fm)
   3. the Earth and the moon (the separation between them can be found in many references)
   Compile your results in a table like the one below.

   	electro­static force (FE)	gravita­tional force (Fg)	order of magnitude comparison (FE/Fg)
   e− and p+ in a hydrogen atom
   p+ and p+ in a helium nucleus
   Earth and moon in space
3. If electric forces are so much more powerful than gravitational forces, why do we feel the Earth's gravitational force and not its electric force?