Hi all, I have become frusturated at a conservation of momentum problem. A space ship(ss) with a mass of 2.0*10^6 [kg] is crusing at a speed of 5.0*10^6 [m/s], when it blows up. One section(s1), with mass 5.0*10^5 [kg] is blown straight backwards at a speed of 2.0*10^6 [m/s]. The second section(s2), with mass 8.0*10^5 [kg], continues forwards at a speed of 1.0*10^6 [m/s]. A third section moves at a certain speed. Trying to find the speed of the third section, I initally approached the problem as a kinetic energy problem, considering that I might be able to use KE=(1/2)mv^2 and simply subtract s1+s2 from ss because the explosion is internal and the change in kinetic energy will be 0: First, the third section has a mass of 7.0*10^5[kg] KE(ss)=2.5*10^19 [J] KE(s1)= 1.0*10^18 [J] KE(s2)= 4.0*10^17 [J] KE(s1+s2)= 1.4*10^18[J] So I subtracted this from KE(ss): 2.5*10^19 [J]-1.4*10^18[J]= 2.36*10^19 [J], which is the KE for the third section Then I set up 2.36*10^19 [J] = (1/2)*(7.0*10^5)(v_s3)^2, and I obtained a velocity for the third section of v_s3= 7.93*10^6 [m/s]! The solution in the back of the book reads 1.46*10^7 [m/s]. So, ok, this is obviously not the correct way to set up this problem, so I did vector sum for momentum using p(vector)=m*v(vector). The space ship has a vector 9.45*10^12 [kg*m/s] Section1 has vector 1.144*10^12 [kg*m/s] Section2 has vector 1.105*10^12 [kg*m/s] Section 3 has mass of 7.5*10^5 [kg]. I subtracted section1+section2 vectors from the space ship vector, and the result was 7.201*10^12 [kg*m/s]. Then I inserted this back into the p(vector)=m*v(vector): 7.201*10^12 [kg*m/s]= 7.5*10^5[kg] * v I solved for v and recieved 9.6*10^6[m/s]. Im obviously not doing something right. I think I may not be factoring in that these are vectors? Thanks for any help.