# Work, Velocity, Friction, and Potential Engery with a sliding block

1. Nov 20, 2008

### Phoenixtears

(Green means correct)

1. The problem statement, all variables and given/known data
In the figure below, a small block is sent through point A with a speed of 8.1 m/s. Its path is without friction until it reaches the section of length L = 12 m, where the coefficient of kinetic friction is 0.70. The indicated heights are h1 = 8.0 m and h2 = 1.1 m.
(Image Attached)

(a) What is the speed of the block at point B?
15 m/s
(b) What is the speed of the block at point C?
14.1 m/s
(c) Does the block reach point D?
---Select--- yes no
If so, what is its speed there and if not, how far through the section of friction does it travel?
in units of m/s

2. Relevant equations

Kinematics equations
Mu*N= Fkinetic

3. The attempt at a solution

Now, I've already finished a, b, c, I just need help with d. I first determined that all I had to do was set up a kinematics graph and use point C as my starting point. So, my inital velocity would be 14.1, my acceleration (which I got from using the second equation above, the normal force is equal to the weight for mg) is -6.86, and my delta-x is 12.

I realize that the picture does not depict L to be 12 exactly, but I see no other way to do this. Then, using the Vf^2=Vo^2 +2ax equation I solved for Vf. My answer was 5.84 m/s, however, this is incorrect. Could someone lead me to the right direction???

~Phoenix

#### Attached Files:

• ###### Block and Work.jpg
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2. Nov 20, 2008

### Staff: Mentor

Looks good to me.

(Perhaps it's a fluke in the online system. Try redoing your calculations without rounding off until the last step.)

3. Nov 21, 2008

### Phoenixtears

Thanks for your response! At least I feel like I know what I'm doing.... I'll redo it right now.

4. Nov 21, 2008

### Phoenixtears

Hmm... turns out I didn't round anything off until the end. And still got the same answer. Perhaps I should merely confront my teacher tomorrow about the incident. Is there anything else I could possibly be doing wrong?