Homework Help: Finding the velocity and covered distance of Astronaut pushing asteroid

1. Oct 14, 2008

soul_observer

1. The problem statement, all variables and given/known data
An astronaut of mass 60 kg and a small asteroid of mass 40 are initially at rest with respect to the space station. The astronaut pushes the asteroid with a constant force of magnitude 250N for 0.35s. Gravitational forces are negligible. A)How far apart are the astronaut and asteroid 5.00s after the astronaut stops pushing? B) What is their relative speed at this time?

2. Relevant equations
TotalForcex=ma
Delta x=(1/2)(delta v)(delta t)
Delta v=a(delta t)

3. The attempt at a solution
1. Total force of x is 250N, so 250N=ma=250N/40= acceleration = 6.25m/s^2
2. (deltax)=(1/2)(6.25)(5.35)^2 = 89.4
3. Vf=(6.25)(5.35)=33.4 m/s

Does this look alright?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Oct 14, 2008

LowlyPion

The astronaut and asteroid are both in space. Don't forget Newton's 3rd Law.

For every action there is a reaction. The 250N force on the asteroid is also a 250N force on the Astronaut in the opposite direction. You need to also take into account the acceleration on the astronaut. The question asks for their distance apart after 5s and their relative speed. (One is going in the opposite direction to the other.)

As to method, you need to figure first the distance apart after the Force stops, then there is the constant velocity over 5s.

3. Oct 14, 2008

soul_observer

So one question before I get going, my professor had said that the total time would be 5.35 and that the wording of the problem is just a bit confusing. Does this sound right? Thanks much for the help!

4. Oct 14, 2008

LowlyPion

It could be seen as ambiguous. The intention is clear though that there is the initial .35s acceleration phase and the 5 second constant velocity phase.

5. Oct 15, 2008

soul_observer

Okay, so I began by analyzing the total forces of both the astronaut and the asteroid. The total forces on the astronaut = -250N = ma so I then found the acceleration of by dividing -250 by mass 60kg to obtain a=-4.17. Doing the same thing for the asteroid I used a postive 250/mass 40kg and obtained an a=6.25. Then I went into obtaining the velocity of both objects so that I could proceed to find the x value. I used the equation deltaV=a(t). I used t=0.35s And for the astronaut I obtained v= -1.46 and asteroid v=2.19. Then I proceed to find x using the equation x=(1/2)(deltaV). The answers I obtained for x were pretty small. So I'm guessing I'm on the wrong track... Do you know what I should or shouldn't do?

6. Oct 15, 2008

LowlyPion

The difference in acceleration between the two is 6.25 and -(-4.17) which is a total of 10.42.

With x = 1/2*a*t2 is .63m

With V2 = 2*a*x that means that the relative V = 3.65 m/s times 5 sec ... plus x ...

7. Oct 15, 2008

soul_observer

Ah ha! I see, okay okay; let's see if I can do this! Thank you so so so much!

8. Oct 15, 2008

soul_observer

Okay, got it. Thank you Very much; I would have been lost without you!