A body A of mass $m = 0.1 \mathrm {~kg}$ has an initial velocity of $3 \hat { \mathrm { i } } \mathrm { m s } ^ { - 1 }$. It collides elastically with another body B of the same mass which has an initial velocity of $5 \hat { \mathrm { j } } \mathrm { m s } ^ { - 1 }$. After the collision, A moves with a velocity $\vec { v } = 4 ( \hat { \mathrm { i } } + \hat { \mathrm { j } } ) \mathrm { m s } ^ { - 1 }$. The energy of B after the collision is written as $\frac { x } { 10 } \mathrm {~J}$. The value of $x$ is $\_\_\_\_$.
A body A of mass $m = 0.1 \mathrm {~kg}$ has an initial velocity of $3 \hat { \mathrm { i } } \mathrm { m s } ^ { - 1 }$. It collides elastically with another body B of the same mass which has an initial velocity of $5 \hat { \mathrm { j } } \mathrm { m s } ^ { - 1 }$. After the collision, A moves with a velocity $\vec { v } = 4 ( \hat { \mathrm { i } } + \hat { \mathrm { j } } ) \mathrm { m s } ^ { - 1 }$. The energy of B after the collision is written as $\frac { x } { 10 } \mathrm {~J}$. The value of $x$ is $\_\_\_\_$.