1.
[tex]dane:\\P = 1,2 \ kW = 1 \ 200 \ W\\t = \frac{1}{4} h = \frac{1}{4}\cdot3600 \ s = 900 \ s\\szukane:\\W = ?\\\\P = \frac{W}{t} \ \ /\cdot t\\\\W = P\cdot t\\\\W = 1200 \ W\cdot900 \ s\\\\W \approx1 \ 082 \ 571 \ J[/tex]
2.
[tex]dane:\\P = 4 \ 200 \ W\\W = 12 \ 000 \ J\\szukane:\\t = ?\\\\P = \frac{W}{t} \ \ \rightarrow \ \ t = \frac{W}{P}\\\\t = \frac{12000 \ J}{4200 \ W}\\\\t \approx2,9 \ s[/tex]
