I've been trying this problem for a while now and can't seem to get the given answer. I know I'm probably making an elementary mistake somewhere but I can't find it.(adsbygoogle = window.adsbygoogle || []).push({});

1. The problem statement, all variables and given/known data

A track is mounted on a large wheel that is free to turn with negligible friction about a vertical axis. A toy train of massmis placed on the track and, with the system initially at rest, the train's electrical power is turned on. The train reaches a steady speed of 0.176 m/s with respect to the track. What is the angular speed of the wheel if its mass is 1.97mand its radius is 0.584 m? (Treat the wheel as a hoop, and neglect the mass of the spokes and hub.) (Answer 0.101 rad/s)

Ok so:

V_{t}= .176 m/s

m_{t}= M

m_{2}= 1.97M

r= 0.584m

I_{2}=m_{2}r^{2}

X_{f}= ?

(X is angular velocity, subscript t for train and 2 for wheel)

2. Relevant equations

L=IX=rmv

L_{i}=L_{f}

L_{t}+L_{2}=0

3. The attempt at a solution

So I set it up with the initial equation

L_{t}= -L_{2}

rm_{t}v_{t}= IX

Then expanded and substituted for corresponding masses

rMv = 1.97Mr^{2}X

M cancels and so does an r, so

v_{t}= 1.97rX

Then substitute the values

.176 = 1.97(.584)(X)

I get a final answer of

X = .153 rad/s

The answer is supposed to be .101 rad/s which I can't seem to get.

Also I used X for angular speed instead of omega because the text formatting wasn't working, and about 4 different symbols showed up instead of omega. Not sure why.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Angular Momentum - Train Placed on a Wheel

**Physics Forums | Science Articles, Homework Help, Discussion**