# Archimedes Principle Quick Question

## Homework Statement

In air, Bob's weight is 687 N. In water, it is 34.7 N.

Determine Bob's average density.

## The Attempt at a Solution

Is it correct to say that (buoyancy force) + 34.7 N = 687 N?

If so then buoyancy force = (density of water)(volume)*9.81 m/s

I can solve for the volume.

Then I can use (density of Bob)(volume)(9.81 m/s) = 687 N do solve for Bob's average density.

Is that right? I just want to make sure it's okay before doing the rest of the problem.

## Answers and Replies

kuruman
Science Advisor
Homework Helper
Gold Member
You are on the right track.

I was just kind of confused because Bob isn't necessarily all under water. If he was half submerged, wouldn't that change things?

I guess because the question doesn't specify, I should just assume Bob's entirely under water...

kuruman
Science Advisor
Homework Helper
Gold Member
Yes, you should assume that. You cannot solve the problem otherwise, unless you know what percent of his volume is under water.

Okay, thank you!