Question

1) A 178 g copper calorimeter contains 601 g of water at 19.2°C. Steam at 100°C is bubbled through the water. After a while, the mass of water in the calorimeter has increased by 9.5 g, and the temperature is 30.3°C.

Use this information to determine an approximate value for the latent heat of vaporization of water( Mg/kg)

2)A solid cylinder of radius 2.36 cm, length 4.98 cm, emissivity 0.839, and temperature 33.9°C is suspended in an environment of temperature 50.7°C.

a. Calculate the cylinder’s net thermal radiation transfer rate( P_{net 1)}

b. If the cylinder is stretched until its radius is 0.426 cm, its net thermal radiation transfer rate becomes P_{net 2}. Determine the ratio P_{net 2}/P_net

 

Answer 1

1)

$(c_c M+c_wm) (t_2-t_1)=L\Delta m+c_w\Delta m(t_3-t_2),\implies$

$L=\frac{(c_cM+c_wm)(t_2-t_1)-c_w\Delta m(t_3-t_2)}{\Delta m}\approx 2.7\frac{MJ}{kg}.$

2)

$A_1=2\pi r_1^2+2\pi r_1h_1=0.01088~m^2,$

$P_1=\sigma \epsilon (T_2^4-T_1^4)=1.0926\frac{W}{m^2},$

$V_2=V_1,\implies h_2=h_1\frac{r_1^2}{r_2^2}=152,84~cm,$

$A_2=2\pi r_2^2+2\pi r_2h_2=0.041~m^2,$

$\frac{P_2}{P_1}=\frac{A_2}{A_1}=3.77.$