# A runner weighs 687 N and 71% of this weight is water. (a) H

## Homework Statement

A runner weighs 687 N and 71% of this weight is water. (a) How many moles of water are in the runner's body? (b) How many water molecules (H2O) are there?

## Homework Equations

n = N/NA
n= m/mass per mole
NA = 6.022E23
F=ma
H: 2*1
O: 16

## The Attempt at a Solution

a)
687/9.8=70.1 g
70.1 * .71 = 49.77 g of h20
49.77/18 u = 2.765

b) 6.022E23 * 2.765 = 1.665

## Answers and Replies

haruspex
Science Advisor
Homework Helper
Gold Member
2020 Award
70.1 g
His mass is only 70.1 grams?! Check your units.
6.022E23 * 2.765 = 1.665
What happened to the E23?

Nathanael
Homework Helper

## The Attempt at a Solution

a)
687/9.8=70.1 g
70.1 * .71 = 49.77 g of h20
49.77/18 u = 2.765
Is this reasonable? A man who weighs 70.1 grams? Must be a world record...

(Posted at the same time as haruspex, oops)

Last edited:
I forgot the formula was in kg

haruspex
Science Advisor
Homework Helper
Gold Member
2020 Award
I forgot the formula was in kg
So does that change your answer?

So does that change your answer?
Yes it did, thanks

haruspex
Science Advisor
Homework Helper
Gold Member
2020 Award
(Posted at the same time as haruspex, oops)
Always happy to have corroboration.