Force over a frictionless Surface

1. Jan 27, 2012

nDever

Hey,

A certain problem in my physics textbook states that a person pushes a crate over a frictionless surface with a constant force.

If the crate accelerates, wouldn't the person eventually have to start running with it in order to keep applying force to it?

2. Jan 27, 2012

PhanthomJay

Yes. But he wouldn't be able to, because he'd fall on the ice first. Perhaps he could push it with constant force from a chopper. Or just let go of the crate and let it move at some constant speed (neglecting resisting forces like air).

3. Jan 27, 2012

technician

Deleting a trivial response

Last edited: Jan 27, 2012
4. Jan 27, 2012

ZapperZ

Staff Emeritus
Physics is difficult enough as it is without worrying about things that really do not matter in trying to understand and tackle this problem. I suggest you concentrate on what really matters.

Zz.

5. Jan 27, 2012

technician

I like your query and will re-post my original response..... he could push with a long stick. I have tried to think of other ways and I am still thinking about it (have lots of time)
To raise the level I would add that conservation of momentum could be used to analyse the resulting motion and I believe that the centre of mass of the system would remain fixed.
However, I do not know what really matters in physics.

Last edited: Jan 27, 2012
6. Jan 27, 2012

AlephZero

@#2, #5: The OP's question doesn't say the person is also standing on the frictionless surface. Think about pushing a crate along a roller track, for example.

Also, what ZZ said.

7. Jan 27, 2012

technician

If he is standing on the frictionless surface this becomes a very interesting physics problem !!!!!

8. Jan 27, 2012

technician

You could attach a string to the far end of the crate, pass it over a frictionless, massless pulley, pull the string back with an attached spring ensuring that the spring extension is constant.
It is a common mistake to assume that you could attach a mass to the string and expect its weight to provide a constant force. Don't get caught by that nDever !!!!

9. Jan 27, 2012

technician

you could tilt the frictionless surface to 30 degrees then the object would experience a constant force of 0.5W (W = weight of crate) down the slope WITHOUT the person touching the crate.......ZZZZZZZ

Last edited: Jan 27, 2012