# Homework Help: Apparent Weight of Astronaut

1. Oct 1, 2012

### mysticbms

1. The problem statement, all variables and given/known data
What is the apparent weight of a 730-N astronaut when her spaceship has an acceleration of magnitude 2.0g in the following two situations. a) just above the surface of Earth, acceleration straight up; b) far from any stars of planets?

2. Relevant equations
Fnet=N-mg=ma

3. The attempt at a solution
W'=N=mg+ma=m(g+a)
=m(g + 2g)
m=730/g
W'=730*3=2190N

The answer in the book is 2200N, not sure if they just rounded and I'm not sure how to answer b.

2. Oct 2, 2012

### SammyS

Staff Emeritus
Yup. They rounded ... apparently to two sig fig

3. Oct 2, 2012

### mysticbms

This book is killing me. Not the first time it had me thinking I got the wrong answer.

4. Oct 2, 2012

### howie8594

b is actually simpler than a. The reason the book tells you that the spaceship is far from any planets or stars is to tell you that there is a negligible amount of gravitational force acting on the ship. Therefore, the only force acting on the astronaut in this situation is the normal force that the spaceship exerts on the astronaut. So instead of having to add the normal force and gravity, it's just the normal force that makes up the net force.

So in that case, N=ma

5. Oct 2, 2012

### D H

Staff Emeritus
In a sense you do have the wrong answer. You only know the acceleration to two places. It's 2.0 g, not 2.00g. Giving too much precision in an answer is a wrong answer.

6. Oct 3, 2012

### mysticbms

Thank you! I didn't think of it that way. That will definitely help me moving forward when comparing answers to the book.