Work on a sliding Block


by danni7070
Tags: block, sliding, work
danni7070
danni7070 is offline
#1
Oct1-07, 04:28 AM
P: 92
1. The problem statement, all variables and given/known data
A block of weight w sits on a frictionless inclined plane, which makes an angle (theta) with respect to the horizontal. A force of magnitude F, applied parallel to the incline, pulls the block up the plane at constant speed.

1)The block moves a distance up the incline. The block does not stop after moving this distance but continues to move with constant speed. What is the total work Wtot done on the block by all forces? (Include only the work done after the block has started moving, not the work needed to start the block moving from rest.)

2)What is Wg, the work done on the block by the force of gravity as the block moves a distance up the incline?

2. Relevant equations

Wtot = the sum of all work factors right ? So I have to find the work from the force going up the ramp, the work from gravity. ??


3. The attempt at a solution

I think the answer to q1 is W-tot = FL + (-wsin(theta))+N (The opposite force of mg = w)

But this is not correct but I don't know why?

Anyone?
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learningphysics
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#2
Oct1-07, 01:53 PM
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P: 4,125
For the total work, what does the work energy theorem say?

for work done by gravity, use work = [tex]\vec{F}\cdot\vec{d}[/tex]
guslergusler
guslergusler is offline
#3
Oct10-07, 09:33 PM
P: 4
love how i got Wgravity wrong...


Wf= -mgcos(theta) * L

(from masteringphysics, your answer is off by a multiplactive factor..)

learningphysics
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#4
Oct10-07, 09:44 PM
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Work on a sliding Block


Quote Quote by guslergusler View Post
love how i got Wgravity wrong...


Wf= -mgcos(theta) * L

(from masteringphysics, your answer is off by a multiplactive factor..)
Wf is work by the force F?

Wf = mgsin(theta)*L

F must be mgsin(theta) acting up the plane.
guslergusler
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#5
Oct10-07, 09:46 PM
P: 4
sorry i meant force done by gravity
learningphysics
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#6
Oct10-07, 09:48 PM
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Quote Quote by guslergusler View Post
sorry i meant force done by gravity
work done by gravity is -mgsin(theta)*L
guslergusler
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#7
Oct10-07, 09:49 PM
P: 4
that's exactly what i put....

but masteringphysics says i'm off by a multiplactive factor,,
learningphysics
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#8
Oct10-07, 10:07 PM
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Quote Quote by guslergusler View Post
that's exactly what i put....

but masteringphysics says i'm off by a multiplactive factor,,
hmmm... did you put in -wsin(theta)*L exactly?
guslergusler
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#9
Oct10-07, 10:56 PM
P: 4
thank you

my fault ... i input -wgsin(theta)*L
learningphysics
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#10
Oct10-07, 11:25 PM
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Quote Quote by guslergusler View Post
thank you

my fault ... i input -wgsin(theta)*L
no prob.


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