I need desperate help with physics. Please. (Graph added).

Question

http://www.webassign.net/mi3/17-053-Ue_graph_positive.jpg

 

The graph above gives electric potential energy as a function of the distance between two electrically interacting objects. What system could this graph refer to? (Select all that apply.)


a)A sodium ion and a chloride ion.

b)Two protons.

c)Two neutrons.

d)A proton and an electron.

e)Two sodium ions.

f)Two chloride ions.

g)Two electrons.

Answer 1

There is no graph for a tutor to look at.  But keep in mind that

 

U(r₁₂) = kq₁q₂ / r₁₂.

 

If U > 0 then q₁ and q₂ must have the same sign.

 

If U < 0 then q₁ and q₂ must have opposite signs.

 

If U = 0 then at least one of the objects is neutral.

 

So look at the graph of U vs. r₁₂.  If it is positive everywhere, pick answers where the charges are either both positive or both negative.  If it is negative everywhere, pick answers where the charges are opposite in sign.  If it is zero everywhere, pick answers where at least one particle is neutral.