Hey is the answer for qn 4 wrong because shouldn't one direction be negative? This answer also flows onto qn 5 and 6 and another person put a different answer. Could you please clarify what the answer to qn 4 and 5 are please? That is the qns and below is the working

TwoSmartCarsareonaooliisionoourse. as E 18ms'l urns" shown. 860 kg 840 kg 4. What is the total initial momentum of the two cars? 4. View answer and explanation 5. The two cars collide and stick together. What Is their velocity immediately after the collision? 5. 6. What is the change in kinetic energy of the twocar system? 6.