When a man increases his speed by `2 ms^(-1)` , he finds that his kinetic energy is doubled, the original speed of the manis

Options

A. `2(sqrt(2)-1)ms^(-1)`
B. `2(sqrt(2)+1)ms^(-1)`
C. `4.5 ms^(-1)`
D. None of these

Answer

B

Explanation

`KE=1/2mv^2," ""Given", v_2=(v_1+2)" " :. " "K_1/K_2=(v_1/v_2)^2`
`implies1/2=(v_1^2)/(v_1+2)^2 ( :.K_2=2K_1)`
`v_1^2+4v_1+4=2v_1^2," " v_1^2-4v-4=0, " " v_1=(4pmsqrt(16+16))/2`
`v_1=(4+sqrt(32))/2=2(sqrt(2)+1)ms^(-1)`