A particle is placed at the point A of a frictionless track ABC as shown in figure. It is gently pushed towards right. The speed of the particle when it reaches the point $B$ is: (Take $g = 10 \mathrm {~m} \mathrm {~s} ^ { - 2 }$ ).\\
(1) $20 \mathrm {~m} \mathrm {~s} ^ { - 1 }$\\
(2) $\sqrt { 10 } \mathrm {~m} \mathrm {~s} ^ { - 1 }$\\
(3) $2 \sqrt { 10 } \mathrm {~m} \mathrm {~s} ^ { - 1 }$\\
(4) $10 \mathrm {~m} \mathrm {~s} ^ { - 1 }$