To find the force exerted by Sarah while using the inclined plane, we can use the formula for work:
\[ \text{Work} = \text{Force} \times \text{Distance} \times \cos(\theta) \]
Where:
- Work is the energy expended (in Joules),
- Force is the force applied (in Newtons),
- Distance is the length of the incline (in meters),
- \(\theta\) is the angle between the force and the direction of motion.
In this case, if we assume that the force is applied parallel to the incline, then \(\cos(\theta) = 1\).
Given:
- Work = 84 Joules
- Distance = 3 meters
We can rearrange the formula to solve for force:
\[ \text{Force} = \frac{\text{Work}}{\text{Distance}} \]
Substituting the values:
\[ \text{Force} = \frac{84 \text{ J}}{3 \text{ m}} = 28 \text{ N} \]
Thus, Sarah expends 28 N of force.
The correct answer is:
28 N