Question

Joseph, Winston, and Franklin are doing an experiment in lab that involves rotational dynamics. Using the apparatus below, Joseph places a disk with a mass of 379 g on the apparatus. Winston then hangs a 15 g mass from the pulley and releases it. The 15 g mass drops and then rises back up, then drops again. They each graph the angular acceleration α as a function of time as the hanging weight drops and rises. Their graphs are shown below. Only one is correct. Identify the correct graph and explain why it is correct. (10 pts). For the incorrect graphs, explain why they are not correct. (two explanations at 10 pts each = 20 pts for this portion; 30 pts total.)

Answer 1

The following graph is correct.

Because when the 15 g mass drops there is a constant torque acting on disk, hence a constant positive angular acceleration is produced. And when mass rises again there is a constant torque acting on disk but now it is opposite in direction hence a constant but negative angular acceleration is acting on disk. and it is continuously repeating.

The following graph is incorrect, because here angular acceleration is varying and it is always positive.

The following graph is incorrect, because initial angular acceleration is positive which indicates that mass is falling, but after some time it become negative and remain negative which indicates that mass is continuously rising.

ct