# Net Force and Friction

1. Feb 26, 2008

### TheBurningMan

Forces/Friction

I'm new, so I'd like to say thanks in advance for helping me. The site wants all answers to the 4th decimal place. Idk how stuff normally works around here, but a small explanation with the answer would help me understand this stuff better.

1. Three forces act on a particle that moves with an unchanging velocity v = (6 m/s) i - (7 m/s) j. Two of the forces are FA = (4 N) i + (5 N) j + (-2 N) k and FB = (-5 N) i + (8 N) j + (-4 N) k. What is the third force?

_____N i + _____N j + _____N k

2. A baseball player with mass m = 76 kg, sliding into second base, is retarded by a frictional force of magnitude 500 N. What is the coefficient of kinetic friction µkin between the player and the ground?

_____

2. I'm unsure because I missed class with an awesome case of food poisoning. -_-

3. I was sick in class, so I'm unsure.

2. Feb 26, 2008

1. $$F_A+F_B+F_C=0$$
2. $$f=\mu_kN$$

3. Feb 26, 2008

### olgranpappy

Ah. Life is suffering. And that's the good part.

Well, I guess the equation you missed which relates weight to frictional force would be
$$F_{\rm fric}=\mu_{\rm kin} m g$$

and for the first question the equation you missed was Newton's First (or is it the 2nd?) Law: A body in uniform motion remains in motion unless acted upon by a (net) Force. Thus the third force you seek must be that which cancels completely the other two.

4. Feb 26, 2008

### olgranpappy

P.S. I think this thread should be in the Introductory Physics forum.