cq_1_201

Phy 231

Your 'cq_1_20.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.

** **

The metal strap used in the Angular Velocity of a Strap experiment is constrained by a vertical push pin to rotate about a hole in a die.  The die is glued in place to a massive tabletop.  A rubber band is attached to a point 15 cm from the axis and stretched so that it exerts a force of 3 Newtons, directed perpendicular to the rod.  If this force is unopposed it will accelerate the system rapidly. You want to attach a second rubber band 5 cm from the axis to prevent the system from rotating. 

How much force will that rubber band have to exert? 

answer/question/discussion: This is a rotational equilibrium problem where we must analyze not just the force, but also the distance the force is applied from the center of mass; therefore, we hav 3 N * .015 m = .45 N*m of torque. To be equal to this at .05 m we need a force of .45 N*m = F * .05 m; therefore, 9 N = F. It is of course to note that while we have units of N*m that this not the same as unit of N*m = Joule.

Once both of these forces are in place and the system is stationary, what (if anything) will happen if the glue holding the die to the tabletop comes loose?

answer/question/discussion: Since the forces are acting only perpendicular to the length of the ruler, and there is no vertical force, in theory, the ruler would simply slide along the tabletop in the direction of the force applied.

** **

15 minutes

** **

&#At least part of your solution does not agree with the solution and comments given at the link below. You should view the solution at that link and self-critique as indicated there.

Solution

This link also expands on these topics and alerts you to many of the common errors made by students in the first part of this course. &#