# Mechanical Engineering Dynamics Problem

1. Nov 8, 2013

### Tribean

1. The problem statement, all variables and given/known data A plastic film moves over two drums. During a 4s interval the speed of the tape is increased uniformly from v0= 2ft/s to v1= 4ft/s. Knowing that the tape does not slip on the drums, determine (a) the angular acceleration of drum B, (b) the number of revolutions executed by drum B during the 4s interval.

2. Relevant equations$v^{2}_{f}$=v$^{2}_{0}$+at
v=r$\omega$
a$_{t}$=r$\alpha$

3. The attempt at a solution I used the first equation to find that the linear acceleration of the tape is 3 ft/s^2. Since it's translating to drum B I would assume that the point that it touches the top of drum B would also have a linear acceleration of 3 ft/s^2 I then used my 2nd equation to figure out the angular acceleration of B by taking its radius of 15 in or 1.25 ft and dividing it from the linear acceleration coming up with 2.4 rad/s^2 but the back of the book states .400 rad/s^2

Where am I going wrong?