Login


10222007, 11:51 AM  #1 
Second Lieutenant
3
Rep 207
Posts 
halp!!!!!!physics
A block is at rest on an inclined plane whose elevation can be varied. The coefficient of static friction is s= 0.42, and the coefficient of kinetic friction is k = 0.18. The angle of elevation is increased slowly from the horizontal. What is the acceleration of the block?
i know f=ma now the question is what the equality of f would be.....ive tried the various identities and i end up with none of the answers provided....mgsintheta(fgx) or the identity of fgxffr(simple algebra doesnt work, so no)... HALP!!!!!!! 
10222007, 12:12 PM  #2 
e90 newbie
21
Rep 447
Posts 
Wow  its been a long time since my high school AP physics class. I did a project on down hill skiing which used these formulas.
I believe the incline has to first be enough to overcome the statisc friction point. At the point static friction is overcome, the kinetic friction will determine how the acceleration is slowed. Good luck  let me know the answer. I'm interested
__________________
E93 IL Blue M3 ZPP, ZCW

Appreciate
0

10222007, 12:16 PM  #3 
Second Lieutenant
3
Rep 207
Posts 
ya...i got that....theta, the point at which it begins to slide, is 22.78 with these coefficients.....now the equality is what i need......im confused as to what the net force equation would be....im assuming that the only one it could be is fgx(component x of gravity)....setting it up as gsintheta=a;which results in a wrong answer

Appreciate
0

10222007, 02:43 PM  #4 
e90 newbie
21
Rep 447
Posts 
gravity as the downward force  acceleration should be angle of descent subtracting the kinetic friction
__________________
E93 IL Blue M3 ZPP, ZCW

Appreciate
0

10222007, 03:11 PM  #6 
Private First Class
5
Rep 191
Posts 
You need to solve the force vectors that act on the block into components that are either perpendicular or parallel to the surface of the incline plane. You can use the sine of the angle to determine the parallel force, and the cosine to determine perpendicular force.
__________________
Scarecrows25
Jet Black E90 328i / 6MT / Sport / Xenons / Split Fold Rear Seat / OEM Chrome Exhaust Tips 
Appreciate
0

10222007, 04:00 PM  #7  
Major General
1871
Rep 8,390
Posts 
Quote:
__________________
Crazy Diamond


Appreciate
0

10222007, 04:23 PM  #8 
Ski bum
139
Rep 6,208
Posts 
I think the answer is "C". Oh wait, I was guessing at your grade.
What's with all the homework posts??? Funny to read, but I'm tired of doing people's homework! Can't your parents help???
__________________
1999 e46 328i Ti Silver / Black[retired] 2007 e90 335xi Jet Black / Black[retired] 2011 e70 X5 35d Vermillion Red / Cinnamon 2011 e92 M3 LeMans / Fox Red extended 
Appreciate
0

10222007, 06:37 PM  #10  
Ski bum
139
Rep 6,208
Posts 
Quote:
I had a Russian prof who couldn't say "free body diagram" to save his life. I'll remember that guy to my dying day! But hey, I can draw the fee biddy damn!
__________________
1999 e46 328i Ti Silver / Black[retired] 2007 e90 335xi Jet Black / Black[retired] 2011 e70 X5 35d Vermillion Red / Cinnamon 2011 e92 M3 LeMans / Fox Red extended 

Appreciate
0

Post Reply 
Bookmarks 
Thread Tools  Search this Thread 

