• Support PF! Buy your school textbooks, materials and every day products Here!

Easy Acceleration / Friction question

  • Thread starter dglenn9000
  • Start date
  • #1

Homework Statement



A roof has an incline of 10 degrees. If the µ of friction between a 50kg box and roof is .15, how fast will the box move?

Homework Equations



Ff=µ * Fn

The Attempt at a Solution



I have no idea how to get this. I know it very easy.
I figured out Fg = 490N (Fg=9.8 * 50kg)
I figured out Fn = 482.56 (Fn=490 cos 10)
I figured out F//=85.09 (F//=490 sin 10)

I figured out the Acceleration with no friction is 1.70 m/s2 85.09/50

Any help is appreciated, thanks
 
Last edited:

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
25,832
249
Welcome to PF!

Hi dglenn9000! Welcome to PF! :wink:
A roof has an incline of 10 degrees. If the µ of friction between a 50kg box and roof is .15, how fast will the box move?
Hint: just use good ol' Newton's second law …

total force (in the direction of the slope) = mass times acceleration :smile:
 
  • #3
18
0
I have a questions : there is an air track and on that track there is a body at rest upon which acts a constant force for a given time it gains a velocity. My question is if that force acts again upon that body for that amount of time will the velocity be 2 times the first velocity? My opinion is that starting from Newtons law v=v0+at, but if we use two times this quation we obtain that v1=at+at=2v0. Am I right?
 
  • #4
tiny-tim
Science Advisor
Homework Helper
25,832
249
Welcome to PF!

Hi DIrtyPio! Welcome to PF! :smile:

(but please start a new thread in future)
… a constant force for a given time … if that force acts again upon that body for that amount of time will the velocity be 2 times the first velocity? My opinion is that starting from Newtons law v=v0+at, but if we use two times this quation we obtain that v1=at+at=2v0. Am I right?
yes, but it's better to look at it from the words of Newton's second law …

force = rate of change of momentum = mass times rate of change of velocity,

so (from the meaning of "rate of change") ∫force times time = mass times change of velocity. :wink:
 
  • #5


Hi dglenn9000! Welcome to PF! :wink:


Hint: just use good ol' Newton's second law …

total force (in the direction of the slope) = mass times acceleration :smile:

That is how I got how fast it will move without friction.

a= F/m
1.70 m/s2= 85.09/50kg

But my question is how do I figure out the acceleration with friction of .15? Where do I apply the .15 in my equation?
 
  • #6
tiny-tim
Science Advisor
Homework Helper
25,832
249
Hi dglenn9000! :smile:

just woke up :zzz: …
… Where do I apply the .15 in my equation?
You multiply it by the normal force to get the (magnitude of the) friction force: Ffriction = µN.

You then chuck the friction force into the "total force" in Ftotal = ma :wink:
 
  • #7
3
0
Hi everyone do you do any problems considering phyisc?
 

Related Threads for: Easy Acceleration / Friction question

  • Last Post
Replies
2
Views
2K
Replies
3
Views
464
  • Last Post
Replies
1
Views
2K
Replies
24
Views
11K
Replies
10
Views
2K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
2
Views
977
Top