1. The problem statement, all variables and given/known data if the distance between the earth and the sun were to be cut in half, what would be the number of days in the year? 2. Relevant equations 3. The attempt at a solution I can solve this question using simple centripetal force = gravitational force of attraction and then halving the radius, thus finding the new velocity and then new time period. That's is easy, and I get the right answer of 129 days. My problem lies in a different approach. Seeing as there is no external torque, why can't we conserve angular momentum? I tried to do so and ended up with 91.25 days instead. I used the m(r x v) formula for angular momentum as it revolves around the sun and I can't seem to find out why it can't be conserved. Any help is appreciated. Thanks!