A bullet of mass 10 g leaves a rifle at an initial velocit of 1000 m/s and strikes a target at the same level with a velocity of 100 m/s. The work done in joule to overcome the resistance of air will be

Options

A. 5000
B. 3750
C. 500
D. 375

Answer

B

Explanation

Work done by a force `=F xx s ="mass (m) " xx " acceleration (a) "xx s`
`therefore W="mass =ms "((d^(2)s)/(dt^(2)))...........(1)`
But `s=1/3 t^(2)`
`therefore (ds)/(dt)=1/3 xx 2t=2/3 t and (d^(2)s)/(dt^(2))=2/3 ..........(2)`
`therefore W=ms (d^(2)s)/(dt^(2)) and t=2s`
` therefore W=3 xx 1/3 t^(2) xx 2/3=2/3 xx 2^(2)=8/3J`