$A$ spring is compressed between two toy carts of masses $m_1$ and $m_2$. When the toy carts are released,the spring exerts equal and opposite forces for the same time $t$ on each toy cart. If the coefficients of friction $\mu$ between the ground and the toy carts are equal,then the ratio of the displacements of the toy carts is:

• A
  $\frac{s_1}{s_2} = \frac{m_2}{m_1}$
• B
  $\frac{s_1}{s_2} = \frac{m_1}{m_2}$
• C
  $\frac{s_1}{s_2} = \left( \frac{m_2}{m_1} \right)^2$
• D
  $\frac{s_1}{s_2} = \left( \frac{m_1}{m_2} \right)^2$