# Two wheels and angular acceleration

• rosstheboss23
In summary, Don tried to use the angular acceleration equations (that are like the kineticmatics equations) to solve for the angular speed of wheel C, but he got incorrect answers because the acceleration is given above.f

#### rosstheboss23

[SOLVED] Two wheels and angular acceleration

## Homework Statement

In the figure below, wheel A of radius rA = 11 cm is coupled by belt B to wheel C of radius rC = 25 cm. The angular speed of wheel A is increased from rest at a constant rate of 1.6 rad/s2. Find the time needed for wheel C to reach an angular speed of 120 rev/min, assuming the belt does not slip. Linear speeds of two rims must be equal.

## Homework Equations

v=wr; a= w(squared)r

## The Attempt at a Solution

v=wr so v1=v2? Then I tried to use this equation w(squared)r=a And then tried using the angular acceleration equations(that are like the kineticmatics equations). The answers I got using these equations though I think should be wrong because the acceleration is give above. Can someone help explain the concept. I can do the brute work if I know.

v=wr so v1=v2? Then I tried to use this equation w(squared)r=a And then tried using the angular acceleration equations(that are like the kineticmatics equations). The answers I got using these equations though I think should be wrong because the acceleration is give above. Can someone help explain the concept. I can do the brute work if I know.
Hey ross,

I'm not quite sure what your saying here, could you show your steps explicitly?

I assumed that velocity was the same for both around the wheels so since the v is the same for w1r1 and w2r2 where w2 is equal to 120rev/min which I convert to roughly 13 rad/s. The radii for both equations are given to be .11m for r1 and .25m for r2 so I solved for equation v2=w2r2 by plugging in 13(.25) and got roughly 3.25 m/s which I used for v1 and solved for angular speed in v1=w1r1. The angular speed for this I got to be roughly around 30rad/s. Then I used the kinematics equation V= Vo +at using 30rad/s for V and 0 for Vo and then for acceleration the 1.6 rad/s(squared) provided. Does this sound like a legitimate way of trying to solve the problem?

I assumed that velocity was the same for both around the wheels so since the v is the same for w1r1 and w2r2 where w2 is equal to 120rev/min which I convert to roughly 13 rad/s. The radii for both equations are given to be .11m for r1 and .25m for r2 so I solved for equation v2=w2r2 by plugging in 13(.25) and got roughly 3.25 m/s which I used for v1 and solved for angular speed in v1=w1r1. The angular speed for this I got to be roughly around 30rad/s. Then I used the kinematics equation V= Vo +at using 30rad/s for V and 0 for Vo and then for acceleration the 1.6 rad/s(squared) provided. Does this sound like a legitimate way of trying to solve the problem?
Your method looks spot on too me Good. Thanks alot. I appreciate your help.

Good. Thanks alot. I appreciate your help.
A pleasure Don't forget to mark the thread as solved when your done, thanks.