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

## 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

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its urgenttt:(

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?

There's no force of friction?

There's no force of friction?
Even if there is, it wont matter since the question is asked only based on gravity.

How are you getting 20sin30?

In particular, the sin30...

You should use the concept of Work-Energy to solve this, since loss in energy is work.

PhanthomJay
Homework Helper
Gold Member
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?

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 ...

How are you getting 20sin30?

In particular, the sin30...
the weight component that acting on the mass

can someone help meee:((

the weight component that acting on the mass
and why are you using sin?

and why are you using sin?
the component will be sin?? should it be?

tiny-tim
Homework Helper
Hi P-Illiterate!

(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)

except it's to the right … gravity acts down (try it! ), 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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Thank you guys :D
I'll be back with another problem soon ... hahahah xD ^-^