1. A rock was thrown at the angle of 30 degrees against the horizontal surface, being given a velocity $\displaystyle V_0=12m/s$. Find the largest height h and the Z - the range of the throw.

2. Two rocks are falling from a roof. The second one begins its fall when the first one has already covered 30cm. Calculate the distance d between these two rocks after 10 seconds counted from the moment the second rock begins its fall.

3. A marble fell from the height h and covered the last 196,2m in 4 seconds. How long was the marble falling? What height was it falling from?

So my thoughts are:

1. $\displaystyle h_{max}=\frac{v_0^2\cdot\sin^2\alpha}{2g}=\frac{14 4*0,25}{2g}=2m$

$\displaystyle Z=\frac{v_0^2\cdot\sin 2\alpha}{g}=\frac{144\sqrt{3}/2}{9,81}=12m$

2. It turns out second rock will go as follows: $\displaystyle s_2=\frac{at^2}{2}={9,81*100}{2}\approx 490,5m$ - where is there an error here? It seems a little weird to me that the rock will cover almost 500 meters. If it does, though, then we have $\displaystyle 0,3=\frac{9,81t^2}{2}$ so $\displaystyle t\approx0,25s$. Then, we know that $\displaystyle v(0,25)=0+9,81*0,25=2,4525m/s$. And finally $\displaystyle s_1=0,3m+2,45*10+\frac{9,81\cdot100}{2}=515,3m$ so they're 24,8 metres apart. Is that OK?

3. How should I approach this? I always end up with two variables ($\displaystyle v_0, s_0$) which I don't know how to calculate.

Could you please help me and check if it's OK?