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~christina~

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**[SOLVED] 400N child on swing**

## Homework Statement

A 400N child is in a swing attatched to ropes 2.0m long

Find the gravitational potential energy of the child earth system relative to the child's lowest position when

a) the ropes are horizontal

b) rope makes angle 30 deg with vertical

c) child is at bottom of circular arc

## Homework Equations

[tex] U_g= mgy[/tex]

## The Attempt at a Solution

**First of all for this question in general would I be finding the Wnet of the system and thus the change in potential energy of the system? Is that what they want when they say "find the gravitational potential energy of the child earth system?**

When they say a "400N child"

does that mean I can consider that the force of the mass and the gravity already multiplied and thus I can just use that in place of mg

When they say a "400N child"

does that mean I can consider that the force of the mass and the gravity already multiplied and thus I can just use that in place of mg

a) I think that the distance y for a would be 2m b/c the ropes are horizontal and thus since the length of the ropes are 2m then it would be logical that the distance traveled would be 2m.

Would I assume that the child is a distance 0.5m above the ground?

I think I would.. assuming they want the net force

Wnet= [tex]\Delta U_g[/tex]

Ui= mgyi = 400N (0.5m)= 200J ====> does that seem sort of large??

**I would like to see if my thinking is correct before I go further..**

Could someone Please help me ?

Thanks

Could someone Please help me ?

Thanks