How Does a Frictionless Incline Affect Crate Acceleration and Wheel Tension?

[CaptFormal]

Homework Statement

A wheel of radius R = 30.0 cm is mounted on a frictionless horizontal axis. A massless cord is wrapped around the wheel and attached to a 4.75-kg crate that slides on a frictionless surface inclined at an angle of 25.0° with the horizontal. The crate accelerates down the incline at 2.4 m/s2.

(a) What is the tension in the cord?

(b) What is the rotational inertia of the wheel about its axis of rotation?

http://schubert.tmcc.edu/enc/66/4bc10f310fba6066d747ea495c942f9f2656106d7ddf2ff5d8b54e0cfacdd98a6596246f7119a41f9feaf3573da3a023248c9ec461bb2c9f6a44610f161f83989339c3411816f6076856c10d8af94242ce73cdf70aa0bc55.gif

Homework Equations

I = MR^2

I = Inertia
M = Mass
R = Radius

The Attempt at a Solution

I thought I could solve for part (b) using the above formula but I am not getting the correct answer. And I am not even sure how to start on part (a). Any help will be appreciated.

 

[Doc Al]

I thought I could solve for part (b) using the above formula but I am not getting the correct answer.

You're not given the mass, nor can you assume that the wheel is a uniform disk. So that won't work. First solve part (a), then use it to solve (b).

And I am not even sure how to start on part (a).

What forces act on the crate? Apply Newton's 2nd law.