# Homework Help: String with 2 masses

1. Aug 9, 2004

### AbsolutDreamcast

Your roommates have lost the TV remote control, and no amount of searching can find it. Rather than buy a new one, you build a low-cost replacement. You attach one end of a small lever mechanism to the TV's channel-changing button. You plan to attach the other end of the lever to a 3.0-m long string that will run from the TV to the couch. When you pull the string tight and pluck your end of the string, a wave will travel down the string and trigger the lever, changing the channel. Your design assumes that you will disturb the string vertically by only 5.0 mm when you pluck it (so that using your "remote" will not require undue exertion) and that your wave will take only 0.20 s to travel horizontally along the string from your hand to the lever (to give quick channel changes). Unfortunately, your roommates have also taken most of your supply of string. All you can find around the apartment are two different pieces of 1.5-m long string; one piece has a mass of 90 g, while the other piece has a mass of just 10 g. You tie the two pieces together to make a combined 3.0-m long string and attach one end of the combined string to the lever mechanism. You then take the other end in hand and head for the couch.

so basically, I understand that the velocity will not be the same through the pieces of string, it will vary. I also understand v=sqrt(F/mu) and find the linear densities of each portion of the string. My question is can the average velocity be used to help find the tension, or should I try and use an equation for SHM, with Acos(kx-wt) or something to that extent? Any help would be greatly appreciated...

2. Aug 9, 2004

### AbsolutDreamcast

nm, i figured it out