1.
[tex]dane:\\P = 900 \ W = 0,9 \ kW\\m = 200 \ g = 0,2 \ kg\\T_1 = 10^{o}C\\T_2 = 100^{o}C\\\Delta T = T_2 - T_1 = 100^{o}C - 10^{o}C = 90^{o}C\\c_{w} = 4200\frac{J}{kg\cdot^{o}C} \ - \ cieplo \ wlasciwe \ wody\\k = 80 gr/kWh\\szukane:\\t = ?\\K = ?\\\\Rozwiazanie\\\\P = \frac{W}{t} \ \ /\cdot t\\\\W = P\cdot t\\oraz\\W = Q = c_{w}\cdot m\cdot \Delta T\\\\P\cdot t = c_{w}\cdot m\cdot\Delta T \ \ /:P\\\\t = \frac{c_{w}\cdot m\cdot \Delta T}{P}[/tex]
[tex]t = \frac{4200\frac{J}{kg\cdot^{o}{C}}\cdot0,2 \ kg\cdot90^{o}C}{900 \ W}=\frac{4200\frac{J}{kg\cdot^{o}C}\cdot0,2 \ kg\cdot90^{o}C}{900\frac{J}{s}}}\\\\\boxed{t = 84 \ s}\\\\W = P\cdot t=0,9 \ kW\cdot\frac{84}{3600} \ h = 0,021 \ kWh\\\\K = W\cdot k\\\\K = 0,021 \ kWh \cdot\frac{80 \ gr}{kWh}\\\\\boxed{K =1,68 \ gr =0,02 \ zl}[/tex]
2.
[tex]dane:\\m = 5 \ kg \ \ (1 \ l \ wody = 1 \ kg)\\T_1 = 20^{o}C\\T_2 = 60^{o}C\\\Delta T = T_2 - T_1 = 60^{o}C - 20^{o}C = 40^{o}C\\c_{w} = 4200\frac{J}{kg\cdot^{o}C}\\szukane:\\Q = ?\\\\Rozwiazanie\\\\Q = c_{w}\cdot m\cdot \Delta T\\\\Q = 4200\frac{J}{kg\cdot^{o}C}\cdot5 \ kg\cdot40^{o}C\\\\\boxed{Q = 840 \ 000 \ J = 840 \ kJ}[/tex]
[tex](1 \ kJ = 1000 \ J)[/tex]
