Question

Energia cinetia a uniu autoturism , la o viteza de 72 km/h este egala cu 300 kj.determina masa vehiculului.

Answer 1

mv²/2 = Ec  ; m= 2Ec/ v²  = 2*300*1000/ 20²  = 1500 kg

 

Answer 2

$E_c=300 \ kJ=300 \ 000 \ J \\ v=72 \ km/h=20 \ m/s \\ \boxed{m-?} \\ \bold{Rezolvare:} \\ \boxed{E_c=\frac{m \cdot v^2}{2}}\\ m \cdot v^2=E_c \cdot 2 \\ m=\frac{2E_c}{v^2} \\ m=\frac{300 \ 000 \ J \cdot 2}{(20 \ m/s)^2} \\ m=\frac{600 \ 000 \ J}{400 \ m^2/s^2} \\ \Rightarrow \boxed{m=1 \ 500 \ kg=\bold{1,5 \ t}}$