A stone is dropped into a pond. Waves in the form of circles are generated and radius of outermost ripple increases at the rate of 5 cm/sec. then area increased after 2 sec is . . .

Options

A. 100 `picm^(2)//sec`
B. `40cm^(2)//sec`
C. `50cm^(2)//sec`
D. `25cm^(2)//sec`

Answer

A

Explanation

We have, `(dr)/(dt)=5` cm/sec
`A=pir^(2)implies(dA)/(dt)=2pir(dr)/(dt)`
`implies(dA)/(dt)=2pi(10)(50)=100picm^(2)//sec`