# Newton's laws problem

1. May 13, 2010

### electricsound

1. What is the weight of an astronaut during lift off, if his actual weight is 750N and the acceleration of the craft is 5g's.
The way I tried to solve it:
F=ma
F= 75(50)
I think I am missing something with that has to do with the upward acceleration....

Last edited: May 13, 2010
2. May 13, 2010

### tiny-tim

Hi electricsound!

Hint: what would his weight be if the acceleration of the craft was zero?

3. May 13, 2010

### electricsound

At zero acceleration it would be 750N,
I cannot understand how to work out problems when acceleration is involved, even after consulting some worked examples in the book. For example problems which involve elevators and finding the weight of an object while accelerating, finding acceleration of a train using a pendulum suspended from the roof of a carriage... Bdw this is not homework, sorry if I mis placed this post, this is the problem I encountered during revision

4. May 13, 2010

### tiny-tim

ok, at 0g it's 750N, so at 5g it's … ?

5. May 13, 2010

### electricsound

I really have no idea how to work it out....

6. May 13, 2010

### tiny-tim

The weight is the reaction force …

find how many forces are there on the astronaut, then use Ftotal = ma

7. May 13, 2010

### electricsound

Thanks a lot mate I understood..
at a= 50ms^-2
W-750= 75(50)
W=3750+750
W=4500N

thanks again......