# help...anyone know anything about physics

1. i am suppose to build a mouse trap car for school...it must go 2m forward, pick up an object and go 2m backwards without touching it. i can get it to go forwards and pick up the object but not backwards. my design is fairly simple..there's a string attached to the axle.. the other end is attached to the part that comes down on the mouse. you pull that part back and wind up the string by turning the axle back. when the part that hits the mouse springs forward, it unravels the string and spins the wheels. but i have no idea how to make it go backwards.

any hot ideas would be appreciated.

2. Reading this post makes me fel really dumb...almost like I was reading Cantonese!!! I have no idea about the car...what you have already figured out sounds pretty damn good!!

Actually, do you think you have a picture of the design? Because I think it would make it easier...

4. LOL let me try this, it's been eleven years since I have last done physics at my secondary school.

As you have said getting it to go forward is easy but to get it to go backwards is more difficult. The way that I am proposing is to use a spring (not an overly taut one) so that it recoils back. This means that you have to calculate the additional length of string being wound to gain more kinetic energy using the three formulae.

Since your spring would be a linear spring the 1st is Hooke's Law to determine the additional force exerted on the spring when it is pulled by 2 metres (= the force required to pull the spring by 2 metres). Joule is defined as the work done to move 1 newton by 1 metre, the additional joule value would be x times 2 metres. Combine this to the total value of the energy required by the car on its own and equate this total to the equation that calculates the energy available through winding the string on your mousetrap car. You may also like to consider using exaggerated numbers to factor in imperfections in your car and the friction.

I gather that you require the car to make the slightest of contact with the object before it goes back but you know what if you can stand a less elegant methodology, just use the spring without any calculation and stick a high-strength magnet on the end of you mousetrap car and another on your object and let the system do the work, LOL.

P.S. It's 1.30am in the morning and I've just managed to unwind all my trading positions + my physics is a bit rusty so my solution may be absolutely shambolic, LOL

5. it looks sort of like this...there's a string connecting the end of the stick to the back axle

thanks annemerrick, bernz and bee bee
i got this idea to cut up and elastic band...and tie one end to the axle and the other to the car and when the car rolls forward, the elastic band will wind up and hopefully create enough tension to send the car backwards....still have a lot of kinks to work out