解：$(1)t=\frac {s}{v}=\frac {0.8\ \text {km}}{ 10\ \text {km/h}}=0.08\ \text {h}$
$(2)G_{1}=mg=1200\ \text {kg}×10\ \text {N/kg}=12000\ \text {N}$
$(3)p=\frac {F}{S}=\frac { 12000\ \text {N}+8000\ \text {N}}{0.08\ \text m^2}= 2.5×10^{5}\ \text {Pa}$
