Question

Un elev cu puterea de 30 W efectueaza un lucru mecanic de 2.7 kilo-juli, calculati cat a lucrat elevul ?

Answer 1

$P=30 \ W \\ L=2,7 \ kJ=2 \ 700 \ J \\ \boxed{t-?} \\ \bold{Rezolvare:} \\ \boxed{P=\frac{L}{t}} \\ \Rightarrow t=\frac{L}{P} \\ t=\frac{2\ 700 \ J}{30 \ W} \\ \Rightarrow \boxed{t=90 \ s}$