Đáp án:

 a> S2=1,64.S1

b> m2=0,5m1

Giải thích các bước giải:

ta có: 
\(\left\{ \begin{align}
  & {{\rho }_{1}};l;R;{{m}_{1}};{{S}_{1}};{{D}_{1}}=8900kg/{{m}^{3}} \\ 
 & {{\rho }_{2}};l;R;{{S}_{2}};{{m}_{2}};{{D}_{2}}=2700kg/{{m}^{3}} \\ 
\end{align} \right.\)

a>
\(R={{\rho }_{1}}\frac{l}{{{S}_{1}}}={{\rho }_{2}}.\dfrac{l}{{{S}_{2}}}\Rightarrow {{S}_{2}}={{S}_{1}}\dfrac{{{\rho }_{2}}}{{{\rho }_{1}}}={{S}_{1}}.\dfrac{2,{{8.10}^{-8}}}{1,{{7.10}^{-8}}}=1,65.{{S}_{1}}\)

b> Khối lượng:
\(\left\{ \begin{align}
  & \text{ }\!\!~\!\!\text{ }{{m}_{1}}={{D}_{1}}.{{V}_{1}}={{D}_{1}}.{{S}_{1}}.l\text{ }\!\!~\!\!\text{ } \\ 
 & \text{ }\!\!~\!\!\text{ }{{m}_{2}}={{D}_{2}}.{{V}_{2}}={{D}_{2}}.{{S}_{2}}.l\text{ }\!\!~\!\!\text{ } \\ 
\end{align} \right.\)

ta có:
\(\dfrac{{{m}_{1}}}{{{m}_{2}}}=\frac{{{D}_{1}}.{{S}_{1}}.l\text{ }\!\!~\!\!\text{ }}{{{D}_{2}}.{{S}_{2}}.l\text{ }\!\!~\!\!\text{ }}\Rightarrow {{m}_{2}}={{m}_{1}}\dfrac{{{D}_{2}}}{{{D}_{1}}}.\dfrac{{{S}_{2}}}{{{S}_{1}}}=\dfrac{2700}{8900}.\dfrac{1,64{{S}_{1}}}{{{S}_{1}}}=0,5{{m}_{1}}\)