i’m unsure if this is 10/10 right but:
The electric field outside a uniformly charged sphere is given by E = kQ/r^2, where k is Coulomb's constant, Q is the net charge on the sphere, and r is the distance from the center of the sphere. Since the electric field is radially inward, the net charge on the sphere must be negative, as the electric field due to a positive charge points radially outward.
The electric field 20 cm from the center of the sphere is given as 1.5*10^3 N/C. Therefore, we have:
1.5*10^3 N/C = kQ/(0.2 m)^2
Solving for Q, we get:
Q = (1.5*10^3 N/C) * (0.2 m)^2 / k
where k = 9.0*10^9 N m^2/C^2 is Coulomb's constant.
Plugging in the value of k, we get:
Q = (1.5*10^3 N/C) * (0.2 m)^2 / (9.0*10^9 N m^2/C^2) = -1.33*10^-8 C
Therefore, the net charge on the sphere is -1.33*10^-8 C.