Mass of the bob of a pendulum is 100g and the length of the string is 1m . The bob is initially held is such a way that the string is horizontal . The bob is then released. Find the kinetic energy of the bob when the string makes an angle of
(i) `0^@` with vertical

Explanation

When the string is horizontal , the height of the bob above its lowest position =1m =100 cm [Fig.1.21].

Energy of the bob at point P
=potential energy of the bob
`mgh =100 xx980xx100`
`=98xx10^5 ` erg.
At `0^@` angle with the vertical , the string holds the bob at its lowermost position. Hence, energy at B= kinetic energy of the bob = initial potential energy `=98xx10^5 `erg.