Question

at what speed necessary to throw up a bricks to cast 3 bricks before returning of casted earlier? it is impossible to throw more than 2 bricks per second.

Answer 1

$$H _ {m a x} = \frac {V ^ {2}}{2 g} - \max h e i g h t,$$

where

$V$ – initial speed

$$t _ {1} = \frac {V}{g}$$ $$t _ {2} = \sqrt {\frac {2 H _ {m a x}}{g}} = \frac {V}{g}$$

$t = t_{1} + t_{2}$ – Total time of flight

$$t = \frac {2 V}{g}$$

$t^{*} = 1 + 1 + 1 = 3$ sec – Time to cast 3 bricks

$$t > t ^ {*}$$ $$\frac {2 V}{g} > 3$$ $$2 V > 30$$

ANSWER:

$V > 15\, \text{m/s}$