A bullet of mass 4.2 gm is moving at certain velocity. If all its kinetic energy liberated is 20 cal, then the initial velocity of the bullet is

Options

A. 100 m/s
B. 200 m/s
C. 10 m/s
D. 20 m/s

Answer

B

Explanation

`K.E=`Heat energy
`(1)/(2)mv^(2)=20xx4.2`
`v^(2)=(2xx20xx4.2)/(m)=(2xx20xx4.2)/(4.2xx10^(-3))`
`=40xx10^(3)`
`v^(2)=400xx10^(2)`
`v=20xx10=20m//s`.