# The frictionless surface

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1. Nov 29, 2016

### Turhan

1. The problem statement, all variables and given/known data
A 60 kg farmer ropes a 300 kg ox. Both are initially at rest, 24 m apart on a frictionless level surface. When farmer ends up pulling the ox towards him, the ox will move

A) 4m, B) 5m, C) 12m, D) 20m, E) 24m .
Can anyone help me solve this?

2. Relevant equations

3. The attempt at a solution

2. Nov 29, 2016

### billy_joule

3. Nov 30, 2016

### Turhan

Okay so in the momentum eq, how do I find out the velocity?

4. Nov 30, 2016

### billy_joule

You can't find the magnitude of the velocity of either the farmer or the Ox.
But you don't need to.. You only need to find the ratio of the velocities.
Show us your attempt and we'll see where you're stuck.

5. Nov 30, 2016

### PeroK

In my opinion, this is one of these silly questions that makes no real sense. You have to know what practical elements the questioner intends you to ignore and what elements to focus on. Physics is supposed to model the real world, but an absurd question like this blatantly ignores the practical realities.

Anyway, you are supposed to concentrate on conservation of momentum. But, once something has momentum on a frictionless surface, it's not going to stop. So, you are supposed to assume that the farmer and ox move very slowly and bump into each other and stop. So, the question is asking how far the ox has moved when they bump into each other.

6. Dec 1, 2016

### Turhan

How am I supposed to find the velocity? This is question from a previous regional olympiad phase.

7. Dec 1, 2016

### PeroK

The velocity is not relevant. That's one of the things you are supposed to know from reading the question.

8. Dec 1, 2016

### haruspex

The speed does not matter for the answer, though I suspect it would matter to the farmer.

9. Dec 1, 2016

### haruspex

Write out the momentum conservation equation, and think of it as a differential equation.