Calculate percentage change in heat output

[physicist93]

Homework Statement

A 500W heating unit is designed to operate on a 115V line. If the line voltage drops to 110V, calculate the percentage drop in heat output.

Homework Equations

R=V^2/P

The Attempt at a Solution

P=V^2/R

Use V=115, then use V=110, use Power P=500...but not sure how

p.s. I am a UK Physics student. I was wondering could you also say whether you are in the UK or US or...

 

[RTW69]

Find the resistance of the heater. Use that value of resistance and 110 volts to find new power output. %=(initial-finial)*100/initial

 

[physicist93]

Thanks that's great! I've done it now

 

[physicist93]

I got an answer of 8.5%! sounds right...

Btw what do people think about the questions on online-exam-solutions?