Given data
*The given height is 8.65 cm
*The number of oscillation is 5 swings
5 swings take 5.87 second
One swing takes the time period is calculated as
[tex]\begin{gathered} T\text{ =}\frac{5.87}{5} \\ =1.17\text{ s} \end{gathered}[/tex]The expression for the time period of the pendulum is given as
[tex]T=2\pi\sqrt[]{\frac{L}{g}}[/tex]*Here L is the length of the pendulum
*Here g is the acceleration due to the gravity
Substitute the values in the above expression as
[tex]\begin{gathered} 1.17=2\times3.14\sqrt[]{\frac{L}{9.81}} \\ L=0.34\text{ m} \\ L=34\text{ cm} \end{gathered}[/tex]