A corn cob (see Fig. 13.17), shaped somewhat like a cone, has the radius of its broadest end as 2.1 cm and length (height) as 20 cm. If each `1 cm^2` of the surface of the cob carries an average of four grains, find how many grains you would find on the entire cob? given radius r`=2.1cm`
height h`=20cm`
so l`=(r^2+h^2)^(1/2)`
`=20.1cm`(approx)
so curved surface area`=pixx2.1xx20.1=132.66cm^2`
so total no of grains`=132.66cm^2xx4=530`grains(approx)

Explanation

given radius r`=2.1cm`
height h`=20cm`
so l`=(r^2+h^2)^(1/2)`
`=20.1cm`(approx)
so curved surface area`=pixx2.1xx20.1=132.66cm^2`
so total no of grains`=132.66cm^2xx4=530`grains(approx)