# Homework Help: Question regarding finding mass given a weight and gravity

1. Mar 4, 2017

### edgarpokemon

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

we did a quiz in my dynamics class, it was very easy i think but there was a problem where we had to find the speed of an object attached to a spring, but that is not my question. The mass had 8 pounds, and the spring constant was in inches, the measurements in inches. To find the weight, was i suppose to use 8/(386.4) or 8/(32.2)? the 386.4 is the value of gravity but in inches

2. Relevant equations

3. The attempt at a solution

2. Mar 4, 2017

### kuruman

From what I gather on the basis of what you say, the weight of the mass is 8 pounds.

3. Mar 4, 2017

### edgarpokemon

sorry, i meant that the weight was 8 pounds. We were suppose to find the mass by dividing the weight by gravity or W/g.

4. Mar 4, 2017

### haruspex

As far as I am aware, from dim recollection and a little web browsing, one pound force = one pound mass * g. So if the weight was 8 lb force then the mass was 8 lb mass.

5. Mar 4, 2017

### TomHart

Or you could convert pounds to wretched slugs: m = w/g = 8/32.2 = 0.249 slugs

6. Mar 4, 2017

### edgarpokemon

right, sorry i meant slugs. well the problem had measurements in inches and the spring constant was inches, so is it correct find the slugs by using gravity but in inches? so 8/386.4?

7. Mar 4, 2017

### haruspex

I think you need to state the whole problem, word for word.

8. Mar 4, 2017

### TomHart

I found this using Google: "A slug is defined as the mass that is accelerated by 1 ft/s2 when a force of one pound (lbf) is exerted on it."
So no, you can't use inches with slugs. You can't mix units; they have to match. I think if it was me, I would convert all of the inch measurements to feet.