# Speed of Separation between 2 masses?

1. Apr 21, 2010

### mneox

1. The problem statement, all variables and given/known data

Outside the International Space Station, a 60 kg astronaut holding a 4.0 kg object (both initially at rest) throws the object at 10 m/s relative to the space station. A 50 kg astronaut, initially at rest, catches the object. What is the speed of separation of the two astronauts?

2. Relevant equations

p = mv
FΔt = Δp

Law of Cons. of Momentum
Pi = Pf

3. The attempt at a solution

Pi = Pf
(4)(10) = (50)(v)
v = 0.8 m/s

which is wrong :( not sure how to approach this question, any help please? thank you!

2. Apr 21, 2010

### rl.bhat

When the astronaut throws the with some velocity, he will recoil. Find the velocity of recoil v of the first astronaut.
For second astronaut,
m1v1 = (m1 + m2)v2.
where m1 is the mass of the object and v1 its velocity. m2 is the mass of the second astronaut and v2 is the combined velocity.
finally the velocity of separation is (v+v2)