Modelová Otázka ID 2666 - 
Odbrzděný železniční vagon o hmotnosti 20 t se samovolně rozjel z mírného kopce a během klesání nabral rychlost 10 m/s. Pod kopcem vagon narazil do budovy stojící na konci kolejí a zabořil se půl metru hluboko do její stěny. Jak dlouho trvalo, než se vagon o stěnu zastavil, jestliže se jednalo o rovnoměrně zpomalený pohyb?
Správná odpověď je: B
Vagon o hmotnosti 20 tun zastavil na dráze půl metru z rychlosti 10 m · s−1. Pro dráhu rovnoměrně zpomaleného pohybu platí vzorec 
, pro rychlost rovnoměrně zpomaleného pohybu platí 
. Protože výsledná rychlost vagonu byla po zastavení rovna 0, druhý ze vzorců se dá upravit na tvar 
, z nějž je možné vyjádřit zrychlení jako 
. Tento výraz lze dosadit namísto zrychlení do vzorce pro dráhu rovnoměrně zpomaleného pohybu, a vyjádřit tak dráhu tohoto pohybu jako:
,
tedy 
. Pro dobu trvání tohoto pohybu tak platí vzorec:
t = (2 · s)/v0 = 1 m/10 m · s−1 = 0,1 s.
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