1. **Problem statement:** A ball is subjected to two forces: 20 N upward and 50 N downward. We need to find the resultant force acting on the ball and its direction. 2. **Formula:** The resultant force $F_{res}$ when two forces act in opposite directions is given by the difference of their magnitudes: $$F_{res} = F_{down} - F_{up}$$ where $F_{down}$ is the downward force and $F_{up}$ is the upward force. 3. **Calculation:** $$F_{res} = 50 - 20 = 30$$ 4. **Direction:** Since the downward force is greater, the resultant force acts downward. 5. **Answer:** - a) The resultant force on the ball is $30$ N. - b) The direction of the resultant force is **downwards**. This means the ball experiences a net force pulling it downwards with a magnitude of 30 N.