Given data
*The space probe with a mass is 4000 kg
*The expels mass from the space probe is M = 3500 kg
*The expels mass moving with the velocity is v = 2000 m/s
*The remaining mass is m = 500 kg
The expression for the velocity of the remaining 500 kg of the probe is given by the conservation of momentum as
[tex]\begin{gathered} P_{i_{}}=P_f \\ 0=mv_1+Mv \end{gathered}[/tex]
Substitute the values in the above expression as
[tex]\begin{gathered} 0=(500)v_1+(3500)(2000) \\ v_1=-14000\text{ m/s} \end{gathered}[/tex]