Final answer:
The magnitude of the electric field at a point on the x-axis with x = 4.0 m is 20 N/C.
Step-by-step explanation:
To determine the magnitude of the electric field at a point on the x-axis with x = 4.0 m, we can use the formula for the electric field due to a linear charge distribution:
E = k * λ / r
Where E is the electric field, k is the Coulomb constant (9 * 10^9 Nm^2/C^2), λ is the linear charge density, and r is the distance from the charge distribution. In this case, the linear charge density is given as 9.0 nc/m (or 9.0 * 10^(-9) C/m) and the distance is 4.0 m.
Plugging in the values, we get:
E = (9 * 10^9 Nm^2/C^2) * (9.0 * 10^(-9) C/m) / 4.0 m
E = 20 N/C
Therefore, the magnitude of the electric field at the point on the x-axis with x = 4.0 m is 20 N/C.