Explanation:
First, we need to calculate the constant force, that is, the ratio between the applied force and the rubber stretch due to the application of the force:
[tex]k=\frac{F}{d}(1)\\k=\frac{6N}{0.04m}\\k=150\frac{N}{m}[/tex]
Now, we can know how far will an 18N force stretch the rubber. From (1):
[tex]d=\frac{F}{k}\\d=\frac{18N}{150\frac{N}{m}}\\d=0.12m=12cm[/tex]
The work done by the external force on the rubber is equal to its elastic potential energy:
[tex]W=\frac{kd^2}{2}\\W=\frac{150\frac{N}{m}(0.12m)^2}{2}\\W=1.08J[/tex]
