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        riddles >> medium >> Cat Scratches
        
(Message started by: THUDandBLUNDER on Apr 13^th, 2003, 2:50pm)

Title: Cat Scratches
Post by THUDandBLUNDER on Apr 13^th, 2003, 2:50pm

One day while waiting for my beautiful new suitcase to come around on the airport conveyor belt, a frightened airport cat came sailing through the air and landed on it with claws outstretched. The suitcase was traveling due north at 3 km/hr and the cat was traveling due east at 5 km/hr when it landed and it naturally slid, thus making scratches. My wife, prone to jealousy, was furious! "I've caught you in a lie!" she screamed. "Those scratches would be curved if they were made by that cat! I know you're just trying to cover up the truth!" Which of the following correctly describes the scratches that would appear on the suitcase if indeed they were made by the cat under the given circumstances?

1) Curved because the belt and the cat were going at different speeds.
2) Curved because the cat would decelerate while sliding across the suitcase.
3) Curved due to the Coriolis force.
4) Straight because the deceleration vector would be colinear with the velocity vector.
5) Straight because the motion of the suitcase was at right angles to the motion of the cat.
6) Straight because the Coriolis force would not operate on a body moving due east.

Title: Re: Cat Scratches
Post by Chronos on Apr 14^th, 2003, 11:30pm

The cat is initially moving due east, but at any finite time after initial contact, it is no longer moving due east, so the Coriolis force would apply. However, the Coriolis effect would be extremely small, well below the threshold of the detector in question (a pair of rather green human eyes). There would also be curvature due to air resistance (assuming that the air is not comoving with the suitcase), and although that would be far greater than the Coriolis force, the effect would still be negligible. So I'm going to say that the only meaningfully correct statement is number [hide]4[/hide].

Title: Re: Cat Scratches
Post by towr on Apr 15^th, 2003, 3:01am

I think 2 or 4 could be the case, depending on the friction properties of the suitcase..
It might not even be the same in both directions (due to texture)

Title: Re: Cat Scratches
Post by aero_guy on Apr 15^th, 2003, 3:06pm

I have to say that I was all for number two and even thought he must have something else in mind when he asked it until I changed reference frames. If the bag is going around a circle on the conveyor belt there is a problem, but consider it going straight.

Now take the reference frame of the bag. As it is not accelerating (and we assume the cat does not move the bag) it is inertial. Thus we have a cat moving 5.8 km/hr over a stationary surface. It slides to a stop along a straight line. While the cat slows, however, it will make a curved course over the ground, but the lines on the bag will be straight.

Title: Re: Cat Scratches
Post by maryl on Apr 15^th, 2003, 3:44pm

Now here's a guess:
If I went flying across a room and landed on a suitcase, and dug my nails into that suitcase-they wouldn't budge, except to dig deeper thus causing the lines to be straight from the force and depth (or whatever you call it). I don't think the direction of the suitcase or anything else would be a factor. That's an opinion from the peanut gallery.