# Homework Help: Power Equation?

1. Oct 16, 2012

### dolpho

Power Equation??

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

An ice cube is placed in a microwave oven. Suppose the oven delivers 135 W of power to the ice cube and that it takes 33200 Joules to melt it. How long does it take for the ice cube to melt?

2. Relevant equations

P = W / T

3. The attempt at a solution

Ok so I know the answer but this is confusing me... A unit of Power is J/second. So if we rearrange the equation and solve for T in minutes it would be.

T = W / P,

T = 135 / 33200 which doesn't give us the right equation to solve it...

Instead it would be 33200 / 135 / 60 = 4.1 minutes, But why when I rearrange the equation doesn't it make sense?

Last edited: Oct 16, 2012
2. Oct 16, 2012

### lewando

Re: Power Equation??

33200 of what units? Badly stated question. "135 of power"?

P = W/T ? What do you think P and W represent?

3. Oct 16, 2012

### dolpho

Re: Power Equation??

Power = Watts / Time, Fixed my typo up above.

Ugh nvm I just went full retard. I read the question wrong. Ty anyway!

4. Oct 16, 2012

### lewando

Re: Power Equation??

Use power = work (or energy) / time. Power has units of Watts.

5. Oct 16, 2012

### dolpho

Re: Power Equation??

Yea that's what confused me... I mixed up watts and work. Ty!

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