`W_{đ1} = \frac{1}{9}W_{đ2}`

`\frac{1}{2}m_1v_1^2 = \frac{1}{9} \cdot (\frac{1}{2}m_2v_2^2)`

`m_1v_1^2 = \frac{1}{9}m_2v_2^2`

`m_1v_1^2 = \frac{1}{9} \cdot (3m_1) \cdot v_2^2`

`\Rightarrow v_1^2 = \frac{1}{3}v_2^2`

`v_1 = \frac{v_2}{\sqrt{3}} \quad \Rightarrow \quad v_2 = v_1\sqrt{3}` (1)

`W_{đ1}' = W_{đ2}`

`\Rightarrow \frac{1}{2}m_1(v_1 + 3)^2 = \frac{1}{2}m_2v_2^2`

`m_1(v_1 + 3)^2 = 3m_1 \cdot v_2^2`

`\Rightarrow (v_1 + 3)^2 = 3v_2^2 `

Thay (1) vào

`(v_1 + 3)^2 = 3 \cdot (v_1\sqrt{3})^2`

`v_1 = 1,5\text{ m/s}`

`v_2 = 1,5\sqrt{3}\text{ m/s}`