Physics help!

[Maxi]

I need to get the "rörelsefrictionskoefficient" (roughly translated movement frictions coefficient) from this task:

A sled is on a horizontal plane, a force of 750N is put on it from the left to the right, it is put in motion with an acceleration of 0.10m/s^2. What is the "rörelsefrictionskoefficient"?

The total mass of the sled is 420 kg.


Any tips? sollutions?

 

[63]

how is it put in motion if the pressure is equal on both sides? that makes equilibrium ;(

 

[Maxi]

A force is put on it from the left (750N) with a acceleration of 0.10M/s^2

 

[Majestic XII]

Is rörelsefrictionskoefficient swedish? I never heard of it

I studie the same thing so maybe i can help you if you gimme some more info.

Too bad i dont have my physics book with me :/

 

[Letters]

Arrr making me do physics! :flame:

Okay...

Net Force (horizontal) = mass * acceleration
Net Force = 420 kg * 0.1 m/s^2
Net Force = 42 N

Which means the friction force is pushing with a force of 708 N opposing the 750 N... I think!

So...

Normal Force = Force(weight) (in this case)
420 kg * 9.8 m/s^2 (gravity) = 4116 N

Now...

Force(friction) = Normal Force * coefficient of friction
708 N = 4116 N * coefficient of friction

Coefficient of Friction = 0.17 (unitless) (2 sig figs)

I think that's it...

 

[Majestic XII]

You got:

F: 750
a: 0.10m/s^2

?: ???

What do you want?

 

[Maxi]

Hmm it might be... Ill let ya know tomorow

 

[Maxi]

Rörelse friktions koefficient, thats what my teacher called it anyway :/

 

[63]

I got one: X2(x) + X3(X4)

 

[marksmanHL2 :)]

Errrr. I will try and remember how you do this....

F = MA
F = UR




..... shite, theres something I need to check..

Bah, i'll be bk in a short while if I dont get distracted

 

[Dedalus]

i think i got the answer. i did A-Level Physics (got an A too :farmer: )

let me know if you need anything explaining, hope i covered everything.

 

[thehunter1320]

i have no idea what any of this stuff is!​

 

[marksmanHL2 :)]

Heheh, I am at AS level Mechanics and Physics and I can't believe I didn't get that!

Well. Time to start learning it a bit more.....

 

[Maskirovka]

just don't forget that there can be two types of frictional coefficients...the static and kinetic.

the one he is referring to is the kinetic.

you can observe this in everyday life by trying to move a heavy object on a smooth surface. if you notice, it's always really difficult to move the object at first, but once it gets moving, it's easier. thus, the coefficient of kinetic (moving) friction is always smaller than the coefficient of static friction.

 

[Dedalus]

Heheh, I am at AS level Mechanics and Physics and I can't believe I didn't get that!

Well. Time to start learning it a bit more.....

it's ok, we did this in AS mechanics too early in our first term, you lot should've done this by now. wait till you get onto circular forces and slopes...

 

[marksmanHL2 :)]

Heheh, I have done both moments and the slope problems. I think the reason I can't do this stuff is because I am sooo knackered...

At least I hope it is



Well, I am gona go sleep... Night all!

 

[JonTheCanuck]

hmmm ok if i had the last equation i'd figure it out but i can help up to a certain point, i just cant remember the appropriate u equation

F=ma
F=420*90.1)
F=42N
750N-42N=708N
then u plug that value into an equation with u and solve

 

[Letters]

Dedalus, the way you have it, the force of friction equals the force applied, in which case, it wouldn't be moving at all...

 

[Dan]

yeah, I get the first answer. 0.172
We do this stuff back in grade 10
Fnet=MA
Fnet=420*0.1
Fnet=42
42=750-Ffriction
Ffriction=708
Fnormal=420*9.8
Fnormal=4116
Fnormal*coefficientoffriction=Ffriction
4116*u=708
u=0.172

 

[Dedalus]

Dedalus, the way you have it, the force of friction equals the force applied, in which case, it wouldn't be moving at all...

erm...point out where i've done that and i'll gladly correct it. i can't see what you're pointing at. µ does not equal Force, nowhere have i said that they are equal, which is what you're saying i have done. i worked out µ, which is the coefficient of friction, it's the opposing force to the Force Applied. if the object wasn't moving then µ would equal 1, but i clearly didn't get that answer, i got 0.18something something, which means the block is moving.

 

[JonTheCanuck]

ok my old post was totally wrong, i look up my equations sheet lol. cant believe i almost forgot this after doing harder ones 3 months ago. Odd how fast people forget things...

F=ma
F=420*90.1)
F=42N
750N-42N=708N
Ff=umg
Ff=u(420)(9.8)
708=u(420)(9.8)
u=0.172

 

[Letters]

erm...point out where i've done that and i'll gladly correct it. i can't see what you're pointing at. µ does not equal Force, nowhere have i said that they are equal, which is what you're saying i have done. i worked out µ, which is the coefficient of friction, it's the opposing force to the Force Applied. if the object wasn't moving then µ would equal 1, but i clearly didn't get that answer, i got 0.18something something, which means the block is moving.

You used 750 N for your friction force when calculating the coefficient... 750 N is the applied force, not the friction force. As you can see, a couple of other people have already come up with the answer I got...

 

[Lucifer Crass]

i think i got the answer. i did A-Level Physics (got an A too :farmer: )

let me know if you need anything explaining, hope i covered everything.

I wish you where my math teacher.

 

[Maxi]

Well the teacher explained the task in school and now I understand it, it uses the formula F=ma .. Anyway Dan got it right first... ded was almost right.. the correct answer is 0.17.

 

[Dedalus]

i knew it...haven't done this in 3 years...i understand where i went wrong though. maybe i should look through my notes before posting help eh...

 

[Maxi]

hehe, I think you should

 

[Letters]

Well the teacher explained the task in school and now I understand it, it uses the formula F=ma .. Anyway Dan got it right first... ded was almost right.. the correct answer is 0.17.

Dan got it first? No one pays attention to me. :dozey:

 

[Maxi]

Woah, sorry, totally missed your post :/

You got it right first meh...

 

[Dulrough]

Dont they have the answers to the problems in the back of the book?

thats where I look...

 

[magnetmannen]

ye. 0.17 is what i get aswell. (well i actually only did a estimate in my head, where i guesses about 0.2) but 0.17 is more like it.

 

[Maxi]

Dont they have the answers to the problems in the back of the book?

thats where I look...

yeah the answers, but what about the calculations?