# Net Force and Friction

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.

Related Introductory Physics Homework Help News on Phys.org
1. $$F_A+F_B+F_C=0$$
2. $$f=\mu_kN$$

olgranpappy
Homework Helper
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. p.s. my bad for posting this in both forums, but I'll delete the threads as soon as I learn this stuff. Thanks again..

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

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

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