# Motion question

1. Aug 12, 2008

### Aaron321

hey every1.. at the moment for a school project a group of mates and i are building a rat trap operated car. This is made by obviously a rat trap with about 5mm diamater front wheels and cds as the rear wheels... this is just a quick explanation. what i need to do is find out how far the car will go and what speed it will be.

i thought that the distance = circumfrence of the back wheels * revolutions of the axle (has the string tied to t).

however im pretty sure this is just finding out the distance the car will travel from start to when the string is fully unwound (not past that). so now im abit confused and trying to find out a way to find out the distance covered from the momentum. but not sure so if anyone has any suggestions it would be appreciated. cheers

note - info on rat/mouse trap operated cars can be found from a google search.

2. Aug 12, 2008

### tiny-tim

Hi Aaron321!

Finding the distance from the momentum is really a matter of experiment.

On a flat floor, theoretically the rat-trap should stay at the same speed, and go an infinite distance (Newton's first law), whatever momentum it has

In practice, it depends on friction, aerodynamic drag, and how wobbly your cds are!

3. Aug 12, 2008

### Topher925

It also depends if you have a one way bearing between the axle and spindle. If the trap is completely sprung, then the car would go no where from momentum unless theres a one way bearing allowing the axle to continue moving.

If you have a force gage, just push the car with it and read the force it takes to push it at a good speed. Then just fudge the numbers and calculate a guess. If you want super accuracy your gonna have to do what tiny-tim suggested experiment.