1. Feb 6, 2005

### Dmt669

An astronaut , 80 KG, is carrying a bag which is 20 KG, walking at a speed of 2 M/S toward a station, He throw the 20 KG bag forward at 6 M/s, what is his final velocity and direction(away from station, toward station)

heres another one

an astronaut is walking at .15 M/S toward a station, he wants to stop, he throws a 2.5 KG rock toward the station , what does a speed of the rock have to be in order for him to stop, thanks

:tongue: :tongue2:

2. Feb 6, 2005

### Galileo

The total momentum is always conserved.
Before the astronaut throws the rock, the total momentum is:
$$p=(m_a+m_b)v$$
where $m_a$ is the mass of the astronaut and $m_b$ the mass of the bag.
What is the total momentum after the astronaut has thrown the rock?

Same reasoning applies to the second question.

3. Feb 6, 2005

### dextercioby

Galileo,u mixed the bag with the rock and hence the problems :tongue2:

Now,after the precious indications given,which could have been put into 4 simple words "APPLY CONSERVATION OF MOMENTUM",what are the results...?

Daniel.

4. Feb 6, 2005

### Curious3141

Apply conservation of momentum, taking care to make sure the signs of the velocities are consistently applied. And show your thoughts and working first.

5. Feb 6, 2005

### Dmt669

i am having trouble finding the final velocity of the astronaut though

6. Feb 6, 2005

### Curious3141

In the first problem, take the direction of travel toward the station as positive.

What is the initial momentum of the astronaut-bag combo ?

What is the final momentum of the bag ?

Therefore what is the final momentum of the astronaut ? Hence what is the final velocity of the astronaut ?

Do the second problem with the same basic principles.

7. Feb 6, 2005

### Dmt669

WHAT Formula should I use

8. Feb 6, 2005

### Curious3141

Do you mean to say that you don't know the definition of momentum ? You've never learned $p = mv$ ?

9. Feb 6, 2005

### Dmt669

is the answer to the first [roblem 4 m/s backwards

10. Feb 6, 2005

### Curious3141

That is not correct. Show the working please.