For Modern Physics with University Physics, Young/Freeman12E question 21.29a, th

Question

For Modern Physics with University Physics, Young/Freeman12E question 21.29a, the question is: what must the sign and charge of a 1.45g particle be to remainstationary when put in an electric field of 650 N/C directeddownwards?
The solutions given by this site says that since the magnitudeof Newtonian force equals Electric Force, mg = qE and they did a simple substitution to solve for q.
My question is: How come Newtonian Force equals ElectricForce? Wouldn't both newtonian force AND the electric force directthe particle downwards? ie. the particle is subject to gravitation,AND the electric field force.. right?
Could someone please explain, thank you. Easy 10 points :) what must the sign and charge of a 1.45g particle be to remainstationary when put in an electric field of 650 N/C directeddownwards?
The solutions given by this site says that since the magnitudeof Newtonian force equals Electric Force, mg = qE and they did a simple substitution to solve for q.
My question is: How come Newtonian Force equals ElectricForce? Wouldn't both newtonian force AND the electric force directthe particle downwards? ie. the particle is subject to gravitation,AND the electric field force.. right?
Could someone please explain, thank you. Easy 10 points :)

Explanation / Answer

The electric field is downward, not the electric force. Since gravity force is downward so the electric force must beupward, it mean that the charge have a negative value.

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