Hi, this is my first post, I've had a look at some examples to try and use them to help with my answer, but I've had no luck so far. I've just started doing physics and not spent much time on this board, so if my formatting/layout anything is a bit dodgy, then please tell me. I Would really appreciate it if somebody could tell me what I'm doing wrong here, as the answer doesn't seem right to me, so here goes... 1. The problem statement, all variables and given/known data A 7000kg wagon travelling at 8m/s runs into the back of a 5000kg stationary van. a)Calculate their combined speed immediately after the collision b)What is the force exerted on the wagon if the time taken to reach their combined speed after the collision is 0.3s? 2. Relevant equations (m1 u1) + (m2 u2) = (m1+m2)v F=m(v-u)/t 3. The attempt at a solution a)Momentum of the truck =56,000kg m/s I've worked out the combined speed (m1 u1) + (m2 u2) = (m1+m2)v v=61,000/12,000 v=5.08m/s (Combined speed after the collision) b)The best I can work out is F=m(v-u)/t (I'm guessing the masses of the 2 vehicles are added together?) so f=m(5.08-8)/t F=(mv-mu)/t F=60,960-96,000/0.3 F=-116,800 N Am I right here, or way off? Any help here will be much appreciated.