# Rotational motion: Find angular displacement when rotation speed is changing

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1. Oct 27, 2014

### mememe1245

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

A torque acts on a wheel rotating at 19.8 rad/s and increases its angular speed to 23.5 rad/s in 11.2 s. Find the angle through which the wheel turns during this time.

2. Relevant equations
omega = theta/time

3. The attempt at a solution
23.5 - 19.8/11.2 = .33rad/s/s --- this is wrong.

2. Oct 27, 2014

### Staff: Mentor

Your thread title is non-descriptive of the thread content. I will change it this time.

Clearly the problem involves a change in rotation speed, so an angular acceleration is involved. You haven't presented any Relevant Equations involving acceleration.

Can you explain your attempt at solution? Use symbols rather than numbers.

3. Oct 27, 2014

### SteamKing

Staff Emeritus
The problem clearly states, "Find the angle ..." Is 0.33 rad/s/s how you measure an angle?

Review your equations for angular motion. There should be one which gives you the angular displacement if you know: the time, the angular velocity, and the angular acceleration.

4. Oct 28, 2014

### Sharath K Menon

You found out the angular acceleration......NOT the angle present.

Try using proper required equations to find out the angle displaced

(Hint:- kinematic equations and equations for circular motions are pretty much the same

Last edited by a moderator: Oct 28, 2014
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