Question

In the movie gravity, astronauts Sandra Bullock & George Clooney are stranded in space and connected by a string. To come closer to each other they both start pulling the string from their ends. Assuming that if the astronauts are pulling the string with a force F then the tension in the string should be equal and in opposite direction and should pull the astronaut (According to Newton's 3rd law).

Then in that case the net force on each astronaut should be 0 and they shouldn't move according to 1st law. Why are the moving towards each other?

• A. Obviously George Clooney will pull with a greater force and that's why they two will come closer.
• B. The question is wrong. This can never happen. In movie they use jet packs to come closer.
• C. They come closer because of gravitational attraction between them the string has nothing to do with this
• D. None of these

Answer 1

The correct option is D

None of these

Lets look at the free body diagrams of both astronauts and the string:

What!

Oh yeah Clooney pulls string with tension T.

Then string will pull Clooney with same force T in opposite direction.

So the only external force on Clooney is T and you remember while drawing free body diagram of a body you only draw the forces that are applied on the body and not by the body.

Also tension in the string remains the same throughout given the string is massless.

So the other end of the string is pulling Bullock with force T so in her free body diagram there will be only T. so both the astronauts have only one force in their free body diagram.

By 1st law if there is an external force on the body then the body at rest will start moving and that's why they come closer