Two masses $m_1 = 10 \text{ kg}$ and $m_2 = 20 \text{ kg}$ are connected by an inextensible string over a frictionless pulley,as shown in the figure. The coefficient of friction of the horizontal surface is $\mu = 0.15$. The minimum mass $m$ that should be placed on top of $m_2$ to stop the motion is:

• A
  $\frac{260}{3} \text{ kg}$
• B
  $\frac{140}{3} \text{ kg}$
• C
  $\frac{100}{3} \text{ kg}$
• D
  $100 \text{ kg}$