| Last revised 1999/11/30 |
#15. You can recognize equilibrium problems by their having all accelerations equal to zero and/or all angular accelerations equal to zero. Approach them by drawing force diagrams, choosing a rotation axis if angular accelerations are zero, and applying F = m a and torque = I alpha. Choose systems and the rotation axis to make the equations as simple as possible.
#20. I find 7 distinct forces in this problem, although some of them are equal to others. Notice that you are not given the radius of the spheres and there is no possible way to determine it, so the sphere size has to drop out.
#24. If you get a generic formula for the results of a weighing, you will do a lot less work. You will be able to apply the generic formula more than once, of course.
#26. What system, i. e. which object, should you choose in this problem?
#29. The crucial point for this problem is choosing the best axis for analyzing the torques. Since nothing is actually rotating or accelerating, the axis can be placed anywhere. Where can you put it so as to have as few as possible nonzero torques involving irrelevant forces?
Try using Cartesian components of vectors rather than magnitudes and angles.
#41. You need to analyze more than one system.
#45. Note the hint in the problem. Since there is a linear accleration, you must put the rotational axis through the center of mass of the car, assuming that you use the car as the system to be analyzed.