PHYSICS會考題!急。

Add magnets on one end of the two trolleys respectively, then the face with the magnets should face each other. Initially, trolley B is at rest, with trolley A is given a certain velocity towards B. When they 'collide' each other, the collision is elastic since no energy is lost to the surroundings. (Actually they don't collide with each other).


Add a ticker-tape behind the trolley. Slightly give the trolley a push on the friction-compensated runway.

After the experiment, observe the dots on the ticker-tape. If the dots are evenly distributed, this shows that the trolley is moving with uniform velocity, which implies the runway is friction-compensated.

2009-02-17 20:12:30 補充：
Not really, in this case, the magnetic force is considered to be an internal force in the system (Action and reaction pairs). Since there is no external force in the system, momentum of the system is conserved.

2009-02-18 07:51:02 補充：
No, because the magnetic force exerted on A by B and that exerted on B by A are action and reaction pairs. This can be considered to be the internal force of the system. Over all in the system, you can regard there is no external force in the system, therefore momentum of the system is conserved.

2009-02-18 07:51:39 補充：
If you only regard trolley A as one system, indeed, the magnetic force exerted on A by B is the external force of A. And hence the momentum of A is not conserved, and vice versa.

2009-02-18 07:52:02 補充：
But we are talking about the whole system. The momentum of the whole system should conserve.

其實車既一邊加個spring 都得