Question

Often times during volcano eruptions the clouds have large static charge buildups that cause lightning to happen. If a rock is ejected by the volcano and it flies to a height of 1795 m, and the clouds have a charge concentration of +40.0 C at a height of 3400 m and ?40.0 C at a height of 1000 m, what is the electric field at the ejected rock?

magnitude	1 N/C
direction	2---Select---downwardupward

Answer 1

Note that      
      
E = kq/r^2      
      
      
where      
k =   8.99E+09   N m^2/C^2
q = the source charge   4.00E+01   C
r = the distance from the source charge   = 1605   m
      
For the positive charge.
      
Thus,      
      
E =    -2.2405E+08   N/C [downward]

For the negative charge, note that      
      
E = kq/r^2  

where      
k =   8.99E+09   N m^2/C^2
q = the source charge   -4.00E+01   C
r = the distance from the source charge =    795   m
      
      
Thus,      
      
E =    -4.523E+08   N/C   [downward]

Thus, the net electric field is the sum of these two,

Enet = -6.76*10^8 N / C, DOWNWARD   [FINAL ANSWER]