If you were to ask me which would have less impulse slamming into a haystack or brick wall, I would say that it depends on the variables involved. For example, if the haystack is made of softer materials such as straw while the brick wall is made of harder materials such as concrete, then the brick wall will likely have less impulse because it can better absorb the impact. However, if both the haystack and brick wall are made of equally hard materials, then the one with more mass will have less impulse because it takes more force to move an object with more mass.