A body is projected at $t = 0$ with a velocity $10 \mathrm {~ms} ^ { - 1 }$ at an angle of $60 ^ { \circ }$ with the horizontal. The radius of curvature of its trajectory at $t = 1 \mathrm {~s}$ is $R$. Neglecting air resistance and taking acceleration due to gravity $\mathrm { g } = 10 \mathrm {~ms} ^ { - 2 }$, the value of $R$ is:\\
(1) 10.3 m\\
(2) 2.8 m\\
(3) 2.5 m\\
(4) 5.1 m