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$\begin{array}{c}{\text { Determine the mass and the weight of the air contained in a room }} \\ {\text { whose dimensions are } 6 \mathrm{m} \times 6 \mathrm{m} \times 6 \mathrm{m} \text { . } \mathrm{gm} \text { . }} \\ {\text { Assume the density of the air is } 1.16 \mathrm{kg} / \mathrm{m} 3}\end{array}$

$6 \times 6 \times 8 m$

$\rho=1.16 \mathrm{kg} / m^ 3$

$m=\rho V=1.16 *(6 \times 6 \times 8)=334.1 \mathrm{kg}$

$w=m g=334.1 * 9.81=3277 N$

$\begin{array}{c}{\text { A } 3 \text { -kg rock is thrown upward with a force of } 200 \mathrm{N} \text { at a location where }} \\ {\text { the local gravitational acceleration is } 9.79 \mathrm{m} / \mathrm{s} 2 .} \\ {\text { Determine the acceleration of the rock, in } \mathrm{m} / \mathrm{s} 2}\end{array}$

$F=m a$

$w=m g \quad=3 * 9.79=29.37 N$

$F_\text { net }=200-29.37=170.6 \mathrm{N}$

$\rho=\frac{F}{m}=\frac{170 \cdot 6}{3}=56.9 \mathrm{m/s}^{2}$

$\text { The constant-pressure specific heat of air at } 25^{\circ} \mathrm{C} \text { is } 1.005 \mathrm{kJ} / \mathrm{kg}^{\circ} \mathrm{C}.$

$\text { Express this value in } \mathrm{kJ} / \mathrm{kg}-\mathrm{K} \text { . }$$\mathrm{J} / \mathrm{g} ^{\circ} \mathrm{C}, \mathrm{kcal} / \mathrm{kg} {-}^{\circ} \mathrm{C}, \text { and } \mathrm{Btu} / \mathrm{Ibm} {-}^{\circ} \mathrm{F}.$

$1.005 \frac{\mathrm{k}_{\mathrm{J}}}{\mathrm{kg} \cdot \mathrm{c}^{\circ}}$

$C_{P}=\left(1.005 \frac{k_{J}}{k g \cdot c^{\circ}}\right)$$\left(\frac{\frac{1 k J}{k g \cdot k}}{\frac{1 k J}{k g \cdot c^{\circ}}}\right)$$=1.005 \mathrm{kg} / \mathrm{kg} \cdot \mathrm{k}$

$C_{P}=\left(1.005 \frac{k J}{k g \cdot c^{\circ}}\right)$$\left(\frac{1000}{1000}\right)=1.005 \ \mathrm{J} / g . \mathrm{c}^{\circ}$

$C_{P}=\left(1.005 \frac{k_J}{k g \cdot c^{\circ}}\right)$$\left(\frac{1 K cal}{4.1868 k J}\right)$$=0.24 \frac{\mathrm{k cal}}{\mathrm{kg} \cdot \mathrm{c}^{\circ}}$