# Homework H5.G - Fa22

Any questions??

Four-step plan

Step 1: FBD
Draw a free-body diagram for the disk.

Step 2: Kinetics - Work/energy
Write down the kinetic energy and potential energy expressions for the disk, along with the work done on the disk by non-conservative forces. Note that point C is the instant center (zero velocity point) for the disk. Because of this, you are able to write down the KE for the disk as Tdisk = 0.5*ICω2, if you choose to do so. The work done by F is equal to U = FsA, where sA is the distance traveled by end A of the cable.

Step 3: Kinematics
Here you need to relate the distance traveled by point O to the distance traveled by end A of the cable (these are not the same). In doing this, recall that C is the instant center of the disk as it rolls without slipping.

Step 4: Solve
Solve your equations from Steps 2 and 3 for the speed of point O.

## 11 thoughts on “Homework H5.G - Fa22”

1. Christian Charlson says:

In order to relate O to A, can we consider them to be on the same rigid body? How else could we relate them?

1. Noah James Willis says:

Assuming you mean relating it for velocity, you can use C as the Instant Center and measure both the velocity of O, and then the point directly above O, which will be equal to the velocity of A.

1. Michael Solmos says:

I think they meant how do you solve for the distance that A travels, not the speed.

1. skfree says:

Once you find the relationship between the velocity of O and the velocity of A, you can integrate that equation to find the change in the distance traveled. For example, if v_B = 2*v_A, then delta_s_B = 2*delta_s_A

2. Michael Solmos says:

How can you solve for the distance that point A travels in relation to O, and why are they not the same?

3. Celena J Haight says:

Do we start by finding the distance of point A to the center O or should we use C as instant center to find the distance and use that to find the velocity of A?

4. Kenneth T Nakayama says:

Since the disk starts at rest and the spring is upstretched does this means that T1 and V1 equal zero?

5. Kenneth T Nakayama says:

Do we leave our answer in terms of d? I still have d in my final equation

6. Enrico Setiawan says:

In the solution video, why was (1/2)mv^2 left out of the final equation (step 4)?