3. Two train cars are to be coupled on the tracks. One of the cars, say A is initially at rest. The other car, say B is travelling at a speed v toward A: Car B is empty, whilst car A is full of pig iron and has a mass of 102mB: After coupling, the two cars travel a distance of 20 meters before coming to rest. The coefficient of static friction of iron-on-iron is 1.1. Assume the tracks are level. (a) What was the initial speed v of car B? (b) How much energy was given up to the coupling process?