1. Given data

   • Initial mass of body: $m_1 = 1000\,\text{kg}$
   • Initial velocity: $u = 6\,\text{m/s}$
   • Extra mass added: $m_2 = 200\,\text{kg}$

2. Physical principle used When extra mass is added to a moving body without external horizontal force, horizontal momentum is conserved.

   Initial momentum: $p_i = m_1 u = 1000 \times 6 = 6000\,\text{kg m/s}$

3. Final mass $M = 1000 + 200 = 1200\,\text{kg}$

4. Apply conservation of momentum Let final velocity be $v$. $p_f = Mv = 1200v$

   Since momentum is conserved, $6000 = 1200v$

   $v = \frac{6000}{1200} = 5\,\text{m/s}$

5. Check options

   • A: $6$ ❌
   • B: $2$ ❌
   • C: $3$ ❌
   • D: $5$ ✅

Therefore, the final velocity is $5\,\text{m/s}$.