Электромотор равномерно поднимает груз массой 30кг с верёвки,при этом развивает мощность 300 вт. с какой скоростью движется груз? 20 !

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Ответ:

nisa89

17.09.2020 22:20

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Ответ:

Dag18y5557hvvhi

26.08.2020 22:39

Все количество теплоты, полученное от сгорания m_c=0.3kg

спирта, пойдет на нагрев m_v=10kg

воды от температуры t_1=20^oC

до температуры t_2

.
$cm_v(t_2-t_1)=q m_c
\\\
t_2-t_1= \dfrac{q m_c}{cm_v} 
\\\
t_2=t_1+ \dfrac{q m_c}{cm_v}$
Удельная теплоемкость воды $c=4200 \frac{Dg}{kg\cdot ^oC}$
Удельная теплота сгорания спирта $q=2.7\cdot 10^7 \frac{Dg}{kg}$
$t_2=20^oC+ \dfrac{2.7\cdot 10^7 \frac{Dg}{kg}\cdot 0.3kg}{4200 \frac{Dg}{kg\cdot ^oC} \cdot 10kg} \approx 212.8 ^oC$
Получившаяся температура больше температуры кипения воды, поэтому вода (или ее часть) превратится в пар.
Оценим, хватит ли выделившегося количество теплоты для того, чтобы превратить в пар всю воду. К затратам на нагревание воды добавим затраты на парообразование:
$cm_v(t_p-t_1)+Lm=q m_c
\\\
Lm=q m_c-cm_v(t_p-t_1)
\\\
m=\dfrac{q m_c-cm_v(t_p-t_1)}{L}$
t_p

- температура кипения воды

- масса воды, которую удастся превратить в пар
$L=2.3\cdot 10^6 \frac{Dg}{kg}$ - удельная теплота парообразования воды
$m=\dfrac{2.7\cdot 10^7 \frac{Dg}{kg}\cdot 0.3kg-4200 \frac{Dg}{kg\cdot ^oC}\cdot 10kg\cdot (100^oC-20^oC)}{2.3\cdot 10^6 \frac{Dg}{kg}} \approx 2.06 kg$
Таким образом, вода нагреется до 100 градусов Цельсия (то есть на 80 градусов Цельсия) и, кроме этого, 2.06 кг превратятся в пар.
ответ: на 80 градусов Цельсия

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