# The laws of motion-a block pulled by a light cord

1. Dec 27, 2013

### haha1234

1. The problem statement, all variables and given/known data
A block of mass 2.20 kg is accelerated across a rough surface by a light cord passing over a small pulley as shown in figure.The tension T in the cord is maintained at 10.0N,and the pulley is 0.100m above the top of the block.The coefficient of kinetic friction is 0.400m.
Determine the acceleration of the block when x=0.400.

2. Relevant equations

3. The attempt at a solution
Are there any mistake?
tanθ=0.4/0.1
θ=76.0°
F-f=ma
10sinθ-0.4x(2.2x9.8-0.1cosθ)2.2a

#### Attached Files:

• ###### DSC_0609-2[1].jpg
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Last edited: Dec 27, 2013
2. Dec 27, 2013

### Staff: Mentor

It is a mistake to present a problem like this without an accompanying diagram, and a mistake to attempt to solve it without drawing a forces diagram to help you.

You also haven't indicated the tension in the cord.

http://imageshack.us/scaled/landing/109/holly1756.gif [Broken]

Last edited by a moderator: May 6, 2017
3. Dec 27, 2013

### haha1234

Sorry.:shy:

Last edited by a moderator: May 6, 2017
4. Dec 27, 2013

### Staff: Mentor

Okay, third mistake, you have attached the wrong pic!

5. Dec 27, 2013

### haha1234

Sorry again.

6. Dec 27, 2013

### tiny-tim

hi haha1234!

what is this?

7. Dec 27, 2013

### haha1234

(2.2x9.8-0.1cosθ) is the normal force of the block.

8. Dec 27, 2013

### tiny-tim

but 0.1cosθ isn't a force, it's a distance

9. Dec 27, 2013

### haha1234

Oh,i have made a stupid mistake.
I can find the correct answer now.
Thank you!

10. Dec 27, 2013

### haha1234

deleted

Last edited: Dec 27, 2013
11. Mar 14, 2016

### Henry Jeong

tanθ=0.1/0.4 <- check it.