Determine the weight of a block

S

staceyrho

Junior Member
Joined
Jan 12, 2007
Messages
76
A block is placed on a inclined plane.
The acceleration of gravity is 9.8 m/s^2
A 28 N force is required to push the block up the incline with constant velocity. Whe is the weight of the block. Anser in units of N.

12degrees 28N

Code: 
    ^this is an arrow going up 
   /
  /     *     *
[W]   *       *  distance from incline 
    *         *  to bottom of triangle
  * u=0.13    *  is 27degrees.
***************
 
Slightly confused about your 'diagram'. Is u the coefficient of friction? Would be better if you uploaded an image from paint possibly.

Anyway, what you want to do is to draw diagram and then resolve the forces perpendicular and parallel to the slope. You will end up with two simulataneous equations; one involing mg and F and the other mg and R. Since the block is moving, F=uR. Substitution would be the final step.
 
the block is moving up the incline at a constant speed ... that should tell you that the net force on the block = 0, because it is not accelerating.


let m = mass of the block
let A = incline angle w/r to the horizontal
let F = 28N applied force pushing the block up the incline
let u = coefficient of kinetic friction
let g = acceleration due to gravity

mgsin(A) = weight component of the block down the incline

mgcos(A) = weight component of the block perpendicular to the incline

f<sub>k</sub> = force of friction down the incline

so ... forces up the incline = forces down the incline ...

F = mgsin(A) + f<sub>k</sub>

now ... f<sub>k</sub> = u*N = u*mgcos(A)

F = mgsin(A) + u*mgcos(A)

you were given everything in the above equation except for m ... solve.
 
I can't figure out what is going on. I really new at all these formula's and for the most part they don't make a ton of sense to me. I am not able to figure out how to plug my numbers into what you have here. Sorry I seem to lost I hate physics and i'm just really trying to get through these next few weeks.
 
If an explanation and complete set-up is not enough to clear up any of the confusion, then it appears as though you need more in-depth assistance than we are able to provide. (We can help students work through specific exercises, but only once the students have a basic grasp of the underlying material.)

Please have a serious talk with your instructor, and/or consider hiring a tutor with whom you can spend a few hours a week, face to face, in order to get caught up.

My best wishes to you.

Eliz.
 
I've tried to sit down with a tutor, but I work full time, I have 3 kids and one on the way very soon. I'm just confused why don't the formulas seem to flow together. it seems like they just don't make any sence. I just need to get through this class before my baby is born. I can't quit the class and i've tried getting help. I just plain out don't seem to understand. Math is my worst subject and this is so much worse than just math alone. I tell you I really hate physics, I just need to get throught the rest of this class somehow.
 
I regret to hear that hands-on in-person tutoring (the best and most intensive sort) has not helped. But this would seem to confirm that you do indeed need more assistance than we would likely be able to offer. Sorry.

My best wishes to you, both in school and for a safe delivery. :D

Eliz.
 
You must log in or register to reply here.
Top