Question

A stone is thrown obliquely upwards with the throw angle 30degree relative to the horizontal plane. the highest point of the path after 0.15s. At what speed was the stone thrown

Answer 1

The time of stone motion to the highest point

$$t=\frac{v_0\sin\theta}{g}$$

So, the initial speed

$$v_0=\frac{gt}{\sin\theta}$$

$$=\frac{9.8\:\rm{m/s^2}\times 0.15\:\rm{s}}{\sin 30^{\circ}}=2.94\:\rm{m/s}$$