A ball having a mass of 100 g and a charge of 4.9 × 10^ -5 C is...

Mass of the ball, $m = 100 \text{ g} = 0.1 \text{ kg}$

Charge on the ball, $q = 4.9 \times 10^{-5} \text{ C}$

Electric field, $E = 2.0 \times 10^4 \text{ N C}^{-1}$

The gravitational force acting on the ball is vertically downwards:

$F_g = mg = 0.1 \times 9.8 = 0.98 \text{ N}$

The electric force acting on the ball is horizontal:

$F_e = qE = 4.9 \times 10^{-5} \times 2.0 \times 10^4 = 0.98 \text{ N}$

Since $F_g$ and $F_e$ are perpendicular to each other, the magnitude of the resultant force is:

$F = \sqrt{F_g^2 + F_e^2} = \sqrt{(0.98)^2 + (0.98)^2} = 0.98\sqrt{2} \approx 1.386 \text{ N} \approx 1.4 \text{ N}$

The angle $\theta$ made by the resultant force with the horizontal is given by:

$\tan \theta = \dfrac{F_g}{F_e} = \dfrac{0.98}{0.98} = 1$

\theta = 45^{}^{{}^{\circ}}