Author Topic: Who's good at sciencey-mathy things? (Read 9131 times)

UncleBob · « **on:** February 24, 2013, 04:39:17 PM »

So, I have a long, straight stretch of road. I'm driving a car at a steady 50 MPH. In front of me is a vehicle going 49 MPH. The back of this vehicle is a ramp. This ramp goes straight up the back of the vehicle, to a platform that goes over the top and then down the front. Like this: /¯¯¯¯¯¯\

Now, this ramp isn't just a normal ramp - it's like a treadmill. If someone stood on the back of this treadmill and was able to stand up straight when the treadmill started moving (while the vehicle is standing still), they'd go forward at 50 MPH.

So, if I'm going 50 MPH, drive onto the ramp-treadmill-vehicle that's going 49 MPH and the treadmill is rolling at 50 MPH - if someone was standing on the side of the road and used a radar detector to measure my speed - how fast would I be going at the top of the other vehicle?

BlackNMild2k1 · « **Reply #1 on:** February 24, 2013, 04:42:24 PM »

you'd be going 49mph...?

BranDonk Kong · « **Reply #2 on:** February 24, 2013, 05:02:29 PM »

149MPH...I think.

ShyGuy · « **Reply #3 on:** February 24, 2013, 05:12:18 PM »

If your speed goes below 55mph you blow up. BUT if you go over 85mph you time travel back to the future.

nickmitch · « **Reply #4 on:** February 24, 2013, 05:58:38 PM »

I think Brandogg is right. You'd move 50 mph relative to the surface you're on (the treadmill), which itself is moving at 50 mph while also being on a platform (the other car) that's moving 49 mph. Right?

pokepal148 · « **Reply #5 on:** February 24, 2013, 06:26:55 PM »

you'd be wasting gas

BranDonk Kong · « **Reply #6 on:** February 24, 2013, 08:45:49 PM »

Pretty sure you just add them all together since they are all going in the same direction.

BlackNMild2k1 · « **Reply #7 on:** February 24, 2013, 09:08:44 PM »

100mph.... ?

I glossed over the part of the treadmill.
But this is he Funhouse, and I didn't really take the question serious enough to read it thoroughly.

pokepal148 · « **Reply #8 on:** February 24, 2013, 09:40:24 PM »

i dont think physics works that way

Stogi · « **Reply #9 on:** February 24, 2013, 10:56:59 PM »

If the treadmill itself is moving 50 mph, it doesn't matter what surface it's on, you would only have to go 50 mph to stay on top of it. The fact that the car is also moving is irrelevant to your question. It's all relative and your speed on treadmill isn't relative to the speed the car. And if you wanted to know what the speed both you and the car are going, well you're on top of the car, so 49 mph.

For instance, we are on flying at damn near a thousand mph simply being on Earth, it doesn't mean I am actually going a thousand mph, though to Mars it would appear so.

Caliban · « **Reply #10 on:** February 24, 2013, 11:01:03 PM »

The real question is, what is UncleBob really planning to do with this setup?

Shaymin · « **Reply #11 on:** February 24, 2013, 11:02:26 PM »

That would be one hell of a Mario Kart tournament.

UncleBob · « **Reply #12 on:** February 24, 2013, 11:15:10 PM »

Quote from: Stogi on February 24, 2013, 10:56:59 PM

If the treadmill itself is moving 50 mph, it doesn't matter what surface it's on, you would only have to go 50 mph to stay on top of it. The fact that the car is also moving is irrelevant to your question. It's all relative and your speed on treadmill isn't relative to the speed the car.

Perhaps I wasn't clear on this point - the treadmill would be pushing you forward in the same direction as both vehicles are traveling - not working against you.

Stogi · « **Reply #13 on:** February 24, 2013, 11:17:38 PM »

So then you'd have to go in reverse to stay on it? Well if it's velocity you want for the car on top, it's negative 50 mph. If it's both, it's still positive 49 mph.

UncleBob · « **Reply #14 on:** February 24, 2013, 11:22:43 PM »

Yeah, you'd have to go in reverse to stay on - but you're not necessarily wanting to stay on. You're wanting to drive off the front of the bottom vehicle.

Stogi · « **Reply #15 on:** February 25, 2013, 12:26:06 AM »

Then yes, you would indeed be going faster than 50 mph once you hit the treadmill. It would be as if you stepped on to a treadmill at the airport. Your speed would increase by 50 mph, i.e. a 100 mph if you kept the same speed. Again the car below you going 49 mph does not add to your own speed.

ShyGuy · « **Reply #16 on:** February 25, 2013, 12:29:33 AM »

Is it like walking up an escalator?

Stogi · « **Reply #17 on:** February 25, 2013, 12:42:01 AM »

Yes, but in this case, we do not have to deal with any incline or decline, since only the speed was given. However, if we were give more facts, you'd have to find the real speed at which the car moves up, over and back down.

In this case, it is more like a car is parked and next to it is a strip of 50 mph treadmill the length of the car. Any speed from another car that reaches the treadmill will simply be added to the 50 mph.

BranDonk Kong · « **Reply #18 on:** February 25, 2013, 01:29:48 AM »

You just add the speeds together - just like walking on a people mover. If it's going at 3 MPH (typical walking speed) and you stay still, then you go at 3 MPH, but if you keep walking in the same direction you go at 6 MPH (notice how you pass people that are standing on it. Now, if that was on top of a car that was also going 3 MPH, you'd be going 9 MPH (relative to the ground).

149 MPH for the car, final answer.

Stogi · « **Reply #19 on:** February 25, 2013, 01:39:21 AM »

No the car on the bottom does not add to the speed. The car has nothing to do with your speed.

That's like saying that stacking 10 cars that are moving the same speed will make the top car 10x faster. It makes no sense.

BlackNMild2k1 · « **Reply #20 on:** February 25, 2013, 01:52:02 AM »

someone put together an illustration.

if the car is moving 49mph, and the treadmill ontop of that car is moving 50mph in the same direction, and then there is a car that drives over that treadmill on the moving car @ 50mph.....

::calculating::

149mph makes sense.

Stogi · « **Reply #21 on:** February 25, 2013, 02:12:12 AM »

Ah ok. I'm am thinking how fast you are going from the perspective of Unclebob, i.e. on top of the ramp. If you were an outside observer, then yes, you would indeed be going 149 mph.

BranDonk Kong · « **Reply #22 on:** February 25, 2013, 09:51:48 AM »

Quote from: Stogi on February 25, 2013, 01:39:21 AM

No the car on the bottom does not add to the speed. The car has nothing to do with your speed.

That's like saying that stacking 10 cars that are moving the same speed will make the top car 10x faster. It makes no sense.

That's only if none of the top cars are moving, they are just sitting there. Not the same thing.

stevey · « **Reply #23 on:** February 25, 2013, 09:29:47 PM »

*Assuming a spherical car in a vacuum cruising at 50 mph*

If the treadmill is realistic, it will grind to a halt from lack of torque and so the car will just continue over the other car at 1 mph and continue pass it going at 50 mph.
Otherwise the treadmill would seem to be going 49mph to the car and fling it forwards at 99 mph; killing everyone in it. The momentum of the wheels wouldn't add to the speed and the engine torque would be spent on preventing the wheels from spinning backwards.

pokepal148 · « **Reply #24 on:** February 25, 2013, 10:03:51 PM »

Quote from: stevey on February 25, 2013, 09:29:47 PM

*Assuming a spherical car in a vacuum cruising at 50 mph*

If the treadmill is realistic, it will grind to a halt from lack of torque and so the car will just continue over the other car at 1 mph and continue pass it going at 50 mph.
Otherwise the treadmill would seem to be going 49mph to the car and fling it forwards at 99 mph; killing everyone in it. The momentum of the wheels wouldn't add to the speed and the engine torque would be spent on preventing the wheels from spinning backwards.

exactly the possibility that i was hinting at

News:

Poll

How fast would the car on top be going, relative to the ground?

Author Topic: Who's good at sciencey-mathy things? (Read 9131 times)