Oscar T. answered 02/09/21
As a physics teacher, I see you have a lot of potential.
Total initial momentum (P_i) before collision:
p_1i (initial momentum of car 1): 2,000kg*20m/s = 40,000kg*m/s
p_2i (initial momentum of car 2): 1,000kg*0 = 0
Total final momentum (P_f) after collision will still be 40,000kg*m/s
P_f = 40,000 = p_1f + p_2f
p_1f = 2,000kg*6.67m/s = 13,340
Therefore:
p_2f = 40,000 - 13,340 = 26,660 = 1000*v_f
v_f = 26.66 m/s