Find distance for gravity to do only -4 J of work

  • #1

Homework Statement


[PLAIN]http://img137.imageshack.us/img137/9280/43448180.jpg [Broken]
find distance for gravity to do only -4 J of work


Homework Equations


[URL]http://buphy.bu.edu/~duffy/PY105/12m.GIF[/URL]
Wg = mgX

The Attempt at a Solution


Can anyone help me from the first stepp
 
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Answers and Replies

  • #4
I know this is wrong because there's no way the answer can be this simple ...

W=F.d
-4 = mgsin30 * d
d = -4/20sin30
d = -.4

.4 to the left

is that even righttt?
 
  • #5
559
8
There's no force of friction?
 
  • #6
424
0
There's no force of friction?
Even if there is, it wont matter since the question is asked only based on gravity.
 
  • #7
26
0
How are you getting 20sin30?

In particular, the sin30...
 
  • #8
424
0
You should use the concept of Work-Energy to solve this, since loss in energy is work.
 
  • #9
PhanthomJay
Science Advisor
Homework Helper
Gold Member
7,164
507
I know this is wrong because there's no way the answer can be this simple ...

W=F.d
-4 = mgsin30 * d
d = -4/20sin30
d = -.4

.4 to the left

is that even righttt?
To the left? Not so simple.......if the work done by a force is negative, what does that imply?
 
  • #10
To the left? Not so simple.......if the work done by a force is negative, what does that imply?
so the mass is going to the opposite direction of force ...
 
  • #11
How are you getting 20sin30?

In particular, the sin30...
the weight component that acting on the mass
 
  • #12
can someone help meee:((
 
  • #15
tiny-tim
Science Advisor
Homework Helper
25,832
251
Hi P-Illiterate! :smile:

(just got up :zzz: …)
I know this is wrong because there's no way the answer can be this simple ...

W=F.d
-4 = mgsin30 * d
d = -4/20sin30
d = -.4

.4 to the left

is that even righttt?
Yes!! (assuming the 20 is correct) :smile:

except it's to the right … gravity acts down (try it! :wink:), so https://www.physicsforums.com/library.php?do=view_item&itemid=75" is positive if you go down, negative if you go up!
 
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  • #16
Thank you guys :D
I'll be back with another problem soon ... hahahah xD ^-^
 

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