Given that the force \( F \) acting on an object varies directly with its acceleration \( a \), we can express this relationship mathematically as:
\[ F = k \cdot a \]
where \( k \) is a constant of proportionality.
From the information given, when the force \( F \) is 50 N, the acceleration \( a \) is 10 m/s²:
\[ 50 = k \cdot 10 \]
To find \( k \), we can rearrange the equation:
\[ k = \frac{50}{10} = 5 \]
Now that we have determined \( k \), we can use it to find the force when the acceleration is 8 m/s². We substitute \( a = 8 \) into the equation:
\[ F = 5 \cdot 8 \]
Calculating this gives:
\[ F = 40 , \text{N} \]
Therefore, when the acceleration of the object becomes 8 m/s², the force acting on it is 40 N.