# Unit conversion difficulties on simple problem

#### xgoddess210

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

A 55 g particle is moving to the left at 27 m/s. How much work must be done on the particle to cause it to move to the right at 41 m/s? Answer in joules

2. Relevant equations

3. The attempt at a solution

27-(-41)=68 , 68*55= 3750

the units here are grams m/s. I need joules. I have no clue on how to make that happen. I can change the g to kg and even get it to newtons (since I know a joule= newton-meter) , but I can't take it any farther. Please help!

#### LowlyPion

Homework Helper
27-(-41)=68 , 68*55= 3750

the units here are grams m/s. I need joules. I have no clue on how to make that happen. I can change the g to kg and even get it to newtons (since I know a joule= newton-meter) , but I can't take it any farther. Please help!
Just convert g to kg in your equation is all you need to do.

#### xgoddess210

I tried that- It gives me an answer of 3.74, but that is wrong. This doesn't really make sense to me.

#### PhanthomJay

Homework Helper
Gold Member
Once you have the correct units, your calculation is nonetheless in error. You have $$W = m\Delta v$$ , which is the change in momentum, not the work done. What is the correct equation to use for Work?

#### xgoddess210

oh! The equation I have for work is W=Fx, but all that is given to me is two velocities and a mass. Force is m*a so w=m*a*x. I guess I'm still at a loss here.

#### LowlyPion

Homework Helper
Oops. That's right. I just thought you were converting units wrong like your title was asking.

Overlooked that it was work and that's not work you have.

What about figuring the change in kinetic energy then?

#### PhanthomJay

Homework Helper
Gold Member
Are you at all familiar with the Work-Energy equation or Conservation of Total Energy equations??

### The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving