$ 解：m_石=ρ_石V=2.5×10^{3}\ \text {kg/m}^3×7\ \text {m}^3=1.75×10^{4}\ \text {kg}=17.5\ \text {t}$
$ m_车=\frac {G_车}{g}=\frac { 49000\ \text {N}}{10\ \text {N/kg}}=4.9×10^{3}\ \text {kg}=4.9\ \text {t}$
$ m_总=17.5\ \text {t}+4.9\ \text {t}=22.4\ \text {t}>20\ \text {t}，所以不能通过$
