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第94页

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$ 解：(1)V_铜=\frac {m_铜}{ρ_铜}=\frac { 1780\ \text {g}}{8.9\ \text {g/cm}^3}=200\ \text {cm}^3$

$ V_球=0.5\ \text {dm}^3=500\ \text {cm}^3$

$ V_铜<V_球，所以是空心的$

$ (2)V_空=V_球-V_铜=500\ \text {cm}^3-200\ \text {cm}^3=300\ \text {cm}^3$

$ 解：(1)m_水=m_冰=ρ_冰V_冰=0.9\ \text {g/cm}^3×80\ \text {cm}^3=72\ \text {g}$

$ V_水=\frac {m_水}{ρ_水}=\frac {72\ \text {g}}{1\ \text {g/cm}^3}=72\ \text {cm}^3$

$ (2)m_水=ρ_水V_水=1\ \text {g/cm}^3×60\ \text {cm}^3=60\ \text {g}$

$ ρ_{盐水}=\frac {m_{盐水} }{V_{盐水}}=\frac {(13.5+60) g}{70\ \text {cm}^3}=1.05\ \text {g/cm}^3$