[单选题]
A 1000-kg car traveling 5l-b(rwvl:ubfqca0nntg 6yl *l (y), at 25 m/s runs into the rear of a stopped car th : fbduvv:q6fi-+tl/6 fr cgl+at has a mass of 1500 kg and they stf:lic6ug6- v+/ffvq : rl+bd tick together. What is the speed of the cars after the collision?