The figure show a simple pendulum consisting a bob of mass 100 g. Initially the bob of the pendulum is at rest at O. It is displaced to one side at A. The height of A above O is 5 cm. (i) What is the value of potential energy of the bob at A? (ii) What is the value of kinetic energy of the bob at position P, whose height above O is 2 cm? (Take `g=10ms^(-2)`)

Answer

(i) 0.05 J (ii) 0.02 J

Explanation

(i) `m=100g=0.1kg,h=5cm=0.05m`,
`g=10ms^(-2)`
`E_(P)` at the point `A=mgh`
`=0.1xx10xx0.05J`
`=0.05J`
(ii) `E_(k)=(1)/(2)mv^(2)`. As the bob swings freely.
`v^(2)=2as=2gh`
`therefore E_(k)=(1)/(2)m(2gh)=mgh`
`=0.1xx10xx0.02J [because h=2cm=0.02m)`
`=0.02J`