# Converting binding energy of an element to joules

1. Dec 9, 2012

### Hannah1

Converting binding energy of an element to joules!!

The binding energy of Mg-24 is 198MeV. What is this value in Joules? Write your answer correct to three significant figures.

MeV = megaelectron volt
1 megaelectron volt = 1.60217646 × 10-13 joules
198 megaelectron volts = 3.17230939 × 10^-11 joules

198 megaelectron volts = 3.17230939 × 10^-11 joules
So, the answer should be 3.17E-11. Correct?

I got the answer wrong on the homework... Could it be because I didn't add the unit to the end of the answer?
Or am I just completely wrong?

2. Dec 9, 2012

### Dick

Re: Converting binding energy of an element to joules!!

The number is correct. But, yeah, an answer in physics without correct units on it is wrong.

3. Dec 11, 2012

### Hannah1

Re: Converting binding energy of an element to joules!!

I added "Joules" to the end of the answer and submitted the homework again, but I still got the answer wrong.

Here are the steps I took to get my answer:

1. I Googled "198 MeV to joules," and Google's built-in calculator gave me "198 megaelectron volts = 3.17230939 × 10-11 joules" as the result.
2. Next, I simplified the number to three significant figures and got "3.17E-11".
3. Finally, I added Joules to the end of my answer, and submitted "3.17E-11 Joules" as my answer.

Is there another way to solve this problem?
What did I do wrong?

4. Dec 11, 2012

### haruspex

Re: Converting binding energy of an element to joules!!

Since it asked for the answer in Joules, it should be expecting just a number. But from another post of yours, it looks like the software is poorly written. Try just "J".