Modelová Otázka ID 2683 - 
Dělová koule o hmotnosti 1 000 g se zabořila do cihlové stěny, přičemž od výstřelu po zastavení ve zdi svému okolí odevzdala celkovou energii 20 kJ. Jak velkou počáteční rychlost koule měla?
Správná odpověď je: B
Dělová koule přijala při výstřelu energii vzniklou chemickou reakcí střelného prachu a dalších částí pohonné složky, aby následně až do okamžiku zastavení ve zdi veškerou přijatou energii odevzdala okolním tělesům a prostředí. V určitém okamžiku krátce po výstřelu byla v ideálním případě veškerá tato energie ve formě kinetické energie dělové koule, pro niž platí vzorec 
. Ze vzorce pro kinetickou energii lze vyjádřit počáteční rychlost koule jako: 
, tedy:
v = √[(2 · EK)/m] = √(40 000 J/1 kg) = √(40 000 m2 · s−2) = 200 m · s−1.
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