# Homework Help: Energy transfers

1. Dec 13, 2011

### Johnboy

1. The problem statement, all variables and given/known data

I am a little confused with energy transfers as the book I am reading is a little vague and I can't seem to find an answer to my question. I have to state the main energy transfers taking place in the following scenario:

(i) A child picks up a wind-up toy (of the type shown in Book 3, Figure 5.9)
from the floor and places it on a table. (ii) He turns the key on the side of the
toy, which winds up a metal spring inside the toy. (iii) The spring unwinds,
causing the toy to move across the table. The toy then slows down because of
frictional forces. (iv) Just as it is stopping, it reaches the edge of the table and
falls to the ground, (v) hitting it with a crash

I am confused with the first stage. In the book it only explains the energy transfer when an object is picked up and thrown into the air. In this situation, the object remains in the hand so I am not sure what type of energy will increase or decrease when it is lifted. Also, when it reaches the edge of the table, is the gravitational potential energy increasing? In the book it again states that this increases as an object's height from the ground increases, which is not happening here.

I know this might be very simple for some but i am new to the whole thing and would be very greatful for a push in the right direction!

Many Thanks

John

2. Relevant equations

3. The attempt at a solution

2. Dec 13, 2011

### BruceW

The main thing is identifying the types of energy in the situation. Then you can go on to find if one type is being converted into another. So a good place to start is to write down the different forms of energy in the scenario.

3. Dec 13, 2011

### Johnboy

Thanks Bruce

The thing is, Im confused as to what the energy conversion is when the toy is placed on the table. Is it chemical potential energy or gravitational potential energy? That is what is confusing me.

4. Dec 13, 2011

### BruceW

This is the bit you're confused with, right? Well, think of what the GPE depends on. This will tell you whether the presence of the hand/table actually is important or not when calculating the GPE.