# Size of the friction force felt?

1. Sep 5, 2015

### EricMatthew

Consider a sled being pulled across the snow at a constant velocity. Imagine that a child pulls the sled with a force of 142 N, and that the rope makes an angle of 32 degrees with the horizontal. The sled moves along the snow with a constant velocity. The sled has a weight of 119 N.

a)Draw a diagram showing all the forces exerted on the sled. Break the forces up into components if needed, draw those forces, and come up with equations for those forces.

b)What is the size of the normal force felt by the sled?

c)What is the size of the friction force felt by the sled?

3. The attempt at a solution
I'm having trouble finding the answer to c and I'm lost as to where to get started.

F1 = 142 N
F1y = 142sin(32)
F1x = 142cos(32)

b. ) Normal force is 119 - 142sin(32) = 118.4

b.) All the tutorials I found online mention two different formulas for kinetic and static and the nature of the question leaves me scratching my head as to which one I should apply. Should I just simply divide the weight of the sled by the normal force as such 119/118.4 since it is going at a constant velocity?

2. Sep 5, 2015

### SteamKing

Staff Emeritus
You should check your arithmetic in the normal force calculation before proceeding ...

3. Sep 5, 2015

### EricMatthew

119 - 142sin (32) = 43.751

Whoops, thank you for that.

4. Sep 5, 2015

### EricMatthew

So what would be a good way to proceed with c.?

5. Sep 5, 2015

### SteamKing

Staff Emeritus
When the sled if being pulled at constant velocity, what must the friction force be, given the amount of pulling force as described in the problem statement?

If you need to, draw a free body diagram of the sled, and remember Newton's First Law of Motion:

http://teachertech.rice.edu/Participants/louviere/Newton/law1.html