Mass of the bob of a simple pendulum is 10g and the effective length is 13 cm. The bob is pulled 5 cm away from the vertical and then released. What will be the kinetic energy of the bob when it passes through the lowest point?

Explanation

From Fig.1.19 we observe that, energy of the bob at point B = potential energy = mgh` =10 xx980 xxAC`. Here OA =OB =13 cm and CB =5 cm.

`therefore OC = sqrt(13^2-5^2)`
=`sqrt(144) =12 cm `
`therefore AC =OA =OC`
=13 -12 =1 cm .
`therefore` Potential energy of the bob at B
`=10xx980 xx1 =9800 erg`
`therefore` Kinetic energy of the bob at the lowest point A = potential energy of the bob at B = 9800 erg.