The volume \( V \) of a rectangular prism can be calculated using the formula:
\[ V = \text{length} \times \text{width} \times \text{height} \]
In this case, the volume \( V \) is 100 cubic units, the height \( h \) is 10 units, and the length \( l \) is 5 units. We can substitute these values into the formula and solve for the width \( w \):
\[ 100 = 5 \times w \times 10 \]
Now, simplifying the right side:
\[ 100 = 50w \]
To find the width \( w \), we divide both sides by 50:
\[ w = \frac{100}{50} = 2 \]
Thus, the width of the rectangular prism is:
\[ \text{width} = 2 \text{ units} \]