What must the charge (sign and magnitude) of a particle of mass 1.46 g be for it to remain stationary when placed in a downward-directed electric field of magnitude 630 N/C?
Use 9.81 m/s^2 for the magnitude of the acceleration due to gravity.

What is the magnitude of an electric field in which the electric force on a proton is equal in magnitude to its weight?
Use 1.67×10-27 kg for the mass of a proton, 1.60×10-19 C for the magnitude of the charge on an electron, and 9.81 m/s^2 for the magnitude of the acceleration due to gravity.

Explanation:

By Newton's first law for an object to remain stationary the net force on it should be zero, so:

, then

(1)

electric force is:

(2)

with q the charge of the particle and E the electric field

and weight is:

(1)

with g the acceleration due gravity and m the mass. Using (3) and (2) on (1)

because electric field is downward directed its sign is negative so:

solving for q

So electric force should be equal to W:

solving for E:

answer: its c lololo

kepler used the data from tycho blahe (his mentor) to construct the laws of planetary motion.