4/12 Misprint in tonight's HW assignment In HW problem #43 in tonight's (4/12) HW, the given equation numbers are wrong. The approximate form is in Eq. (12-18). The exact form can be derived from Eq. (12-17). 4/03 Misprint in tonight's HW assignment In HW problem #55 in tonight's (4/3) HW, the correct radius of the disk is 12 cm or 0.12 m (not 0.12 cm). 3/31 Some comments are necessary for a few of the HW problems at the end of Chapter 9. #47 The initial angular velocity of the bicycle wheel is said to point in the up direction. This is correct, however we will not discuss this use of vectors with angular quantities until Chapter 10. For our purposes, 'up' means CCW when viewed from above, and 'down' means CW when viewed from above (or CCW when viewed from below). #65 and #67 The picture of the yo-yo in problem 65 might not be clear. The yo-yo consists of two uniform discs connected by (and separated by) a "massless" peg of radius r about which the string is wound. The total mass of the yo-yo is M and the radius of the uniform discs is R. So the rotational inertia of the yo-yo is the same as the I for a single uniform disc of mass M and radius R, (1/2)MR^2. 3/06 Misprints in tonight's HW assignment: #44(b) The 1.22 m height should be 0.75 m. #64 The 6.0 cm length should be 60 cm. 2/23 The solutions for TEST TWO (green form) are now available at the Noble Library Copy Center. 2/15 Change to office hours and upcoming help session: Beginning this week my Monday afternoon office hour (3:40-4:40) is cancelled and replaced with an hour on Thursday afternoons from 2:40-3:40, still in PSF-430. There will be a nighttime help session at 7PM in PSF-173 on Thursday 2/17. No test hints will be given, no new material will be covered, and I will not do HW problems. I WILL answer your questions about concepts that you do not understand. 2/08 The solutions for TEST ONE (green form) are now available at the Noble Library Copy Center. 2/02 There will be a nighttime help session at 7PM in PSF-173 on Thursday 2/03. No test hints will be given, no new material will be covered, and I will not do HW problems. I WILL answer your questions about concepts that you do not understand. 1/19 The tests, with solutions, for this instructor's offering of PHY 121 during the first Summer Session 1999 are now available at the Noble Library Copy Center.