# Homework Help: Coin Rolling Up Incline, no mass given?

1. Nov 15, 2004

### splinter

Coin Rolling Up Incline, no mass given!?

1. [SFHS99 8.P.46.] A coin with a diameter of 3.40 cm rolls up a 27.0° inclined plane. The coin starts with an initial angular speed of 55.0 rad/s and rolls in a straight line without slipping. How far does it roll up the inclined plane?

Having some troubles with this problem, since it doesnt give the mass of the object. I have no problems doing this type of problem when a mass is given, I just use the formula a = (mg sin0)/(m+(I/R^2)), then convert that to angular acceleration, and use angular kinematic equations to find the delta theta, and convert that into a meter value by multiplying the radius by the angular displacement. That doesn't work here though, since I have no mass! Any help would be greatly appreciated, thanks!

2. Nov 15, 2004

### CartoonKid

You have to use potential energy and angular kinetic energy to get the answer. Don't worry about the mass, it'll be cancelled in the end of your calculation.

3. Nov 16, 2004

### splinter

Used KEi = PEf, solved for KEi and PEf, got KEi = .2186M, and PEf = 9.81MH. Since KEi = PEf, .2186M = 9.81MH, the mass on each side cancel out, so .2186 = 9.81H, then solve for H, i got .0223 meters, then divide that by sin(27) to get the value of the hypotenuse, which gave me .0491 meters for my answer, which the online homework is telling me is wrong! Sorry if this didn't make much sense I'm rushed in typing it.

4. Nov 16, 2004

### Justin Lazear

Don't forget that the coin has more than just rotational kinetic energy in the beginning. It also has some translational kinetic energy in the beginning.

--J

5. Nov 16, 2004

### CartoonKid

Your KEi is wrong. The I should be 1/2mr^2+mr^2