1. The problem statement, all variables and given/known data 2. Relevant equations ∑F=ma 3. The attempt at a solution This is a problem that can be solved by looking at impulse and momentum and I understand how the problem is solved in the book but I'm wondering about the reasoning before, if this is the only way to look at it. When I look at the picture of what happens, there is a bullet that hits a pendulum so it moves upwards. I would from looking at this assume that when the object (bullet + ballistic pendulum) moves upwards, there is a force of gravity involved. In the way the task has been solved in the book they didn't draw in a free body-diagram showing the forces acting on the objects. What I'm wondering is wouldn't the force of gravity actually be involved after this collision, when the pendulum moves upwards? And then shouldn't it be drawn in a free body diagram?