a
Horizontal component of velocity along \(x\)-axis after \(1 s\) is

\(v _{ x }= u _{ x }+ gt\)

\(v _{ x }= u \cos \theta+0 \times 1\)

\(v _{ x }=30 \cos 30^{\circ}\)

\(v _{ x }=15\sqrt3\; m / s\)

Vertical component of the velocity along \(y\)-axis after \(1 s\) is

\(v _{ y }= u _{ y }- gt\)

\(v _{ y }=30 \sin 30^{\circ}-10 \times 1\)

\(v _{ y }=15-10\)

\(v _{ y }=5 m / s\)

Velocity of a body after 1 s is

\(\overrightarrow{ v }= v _{ x } \hat{ i }+ v _{ y } \hat{ j }\)

\(\overrightarrow{ v }=15\sqrt3 \hat{ i }+5 \hat{ j }\)

Magnitude, \(v =|\overrightarrow{ v }|=\sqrt{(15\sqrt3)^{2}+(5)^{2}}\)

\(v =\sqrt{700}\)

\(v =10 \sqrt{7}\; m / s\)