Răspuns:
C) 40 secunde
Explicație:
formula puterii mecanice [tex]\boxed{P = \frac{L}{\Delta t}}[/tex]
[tex]\displaystyle{ \Delta t = \frac{L}{P} = \frac{mgh}{P} }[/tex]
[tex]\displaystyle{ \Delta t = \frac{4000 \cdot 10 \cdot 20}{20 \cdot 1000} }[/tex]
[tex]\displaystyle{ \Delta t = \frac{800.000}{20.000} = 40 \ s }[/tex]
