AP Solution Sheets and Labs

1) Dennis has pointed out that there is an error on the solution sheet for rotational motion. In the problem where the pivot for the plank is 1 m from the end of the 7 m plank and we are looking for M2, the torque due to the mass of the plank should be taken as clockwise, i.e. as acting on the same side of the pivot as M2g.

2) For the conservation of momentum lab many section 4 reports discuss how momentum appeared to increase after some of the collisions and how friction cannot explain this since there is a gain not a loss.  Examine these cases and see if  p' includes a negative term as cart 1 bounces back after the collision. Is it because this negative term is too low due to friction on cart 1 that the momentum appears to be higher after the collision? Let me know in class or by email what you find.