PLC Activity #8
Rotations & Newton's 2nd Law
Due: Tuesday, April 19th by 4:00 pm
Objectives
Practice applying rotations & Newton's 2nd law to Physlets and Ranking problems.
What to Use
Web browser in the PLC and white board
What to Do
Work with one or more partners in the PLC. Do your calculations, initial sketches and other work as a group on a whiteboard so you can discuss them with your partners and show them to the tutor.
Part 1: Rotation Physlets
Go to Chapter 10: Rotations about a Fixed Axis. Do the following Physlet Physics exercises and answer the questions listed.
Physlet Problem 10.5
A boy sits on a merry-go-round at the position marked by the red circle. A girl gives the merry-go-round a constant tangential push for 0.2 s as shown in the animation (position is given in meters and time is given in seconds). What is the magnitude of the tangential acceleration of the boy while the girl is pushing the merry-go-round?.
Physlet Problem 10.11
a 1.0-kg cart on a low-friction track is connected to a string and a 0.5-kg hanging objects as shown (position is given in meters and time is given in seconds). The pulley has a uniform mass distribution in the shape of a disk and therefore affects the motion of the system.
a. What is the acceleration of the system?
b. What is the tension in the string? (There are two regions of the string to consider.)
c. What is the mass of the pulley?
d. What is the rotational inertia of the pulley?
Part 1: Ranking Questions
Question 1
Plots of angular position q versus time t for three cases in which a disk is rotated like a merry-go-round. In each case, the rotation direction changes at a certain angular position qchange. (a) For each case, determine whether qchange is clockwise or counterclockwise from q = 0, or whether it is at q = 0. For each case, determine (b) whether ω is zero before, after, or at t = 0 and (c) whether α is positive, negative, or zero.
Question 2
In the overhead view, five forces of the same magnitude act on a strange merry-go-round; it is a square that can rotate about point P, at midlength along one of the edges. Rank the forces according to the magnitude of the torque they create about point P, greatest first.
Question 3
What happens to the initially stationary yo-yo if you pull it via its string with (a) force F2 (the line of action passes through the point of contact on the table, as indicated), (b) force F1 (the line of action passes above the point of contact), and (c) force F3 (the line of action passes to the right of the point of contact)?
How to get credit for this activity
Show your answers to a PLC tutor so they can check them and initial the signoff sheet. Be prepared to answer questions about the activity or your results.
2