physics puzzle no.2

noseall · 11 May 2008

an object is stood on a conveyor with magical friction free wheels and bearings.

the front of the object is attached, via a cable to a winch.

the winch is anchored to the ground and cannot be pulled free.

the conveyor matches the speed of the wheels.....blah, blah, blah.

you get the picture.

do any of you doubters believe for a second that the winch will not wind the object in, regardless of what the runway and wheels are doing?

the engines react with the AIR. (ref. other post)

JohnD · 11 May 2008

oops, you still say "conveyor matches the speed of the wheels" which cannot be achieved with a vehicle that is not driven by wheel traction.

Surely it is because the question is defective, and does not make sense, that people are unable to agree on a soultion to it?

doitall · 11 May 2008

Yet again you are forgetting one small point.

You can stand the magical object on the belt and hook it up to your winch.

Start the belt up and the wheel will turn at exactly the same speed as the belt, to make any gain from its position on the belt, the wheels have to go faster than the belt.

All the time the speed of the wheels are the same as the belt, the object will not move.

What is so difficult to understand

blondini · 11 May 2008

If there were absolutely no friction in a magical friction free world, then the wheels wouldn't turn at all. They would just slide if the object were dragged.

doitall · 11 May 2008

doitall said:
Thrust, friction, jet or battery powered it's irrelevant to the topic

The trolley is being held on the belt and the wheels are turning at the same speed as the belt.

The trolley cannot move forward unless the wheels are faster than the belt.

Same answer as part 1

Add what you like to the equation, if the wheels are the same speed as the belt the object will not move

JohnD · 11 May 2008

And if the object does not move, and is not propelled by traction through the wheels, neither the wheels nor the belt will move.

The question is faulty and cannot be solved.

doitall · 11 May 2008

You are missing the point, it doesn't matter, if the question is faulty, it doesn't matter if the winch can pull the object or how you power the object, it doesn't matter if we talking about a Dinkie toy or a 747.

Provided the wheels are the same speed as the belt it won't move.

You can hold your toy on Tesco's checkout conveyor all day long if you like.

if the toy moves in the same direction as the belt the wheels are slower than the belt, if you move in the opposite direction the wheels are faster than the belt

empip · 11 May 2008

noseall said:
an object is stood on a conveyor with magical friction free wheels and bearings.

the front of the object is attached, via a cable to a winch.

the winch is anchored to the ground and cannot be pulled free.

the conveyor matches the speed of the wheels.....blah, blah, blah.

you get the picture.

do any of you doubters believe for a second that the winch will not wind the object in, regardless of what the runway and wheels are doing?

the engines react with the AIR. (ref. other post)

Nah, the aero surfaces use the air for lift -- The jet motor uses air fuel mixture in the old Suck - Squeeze - BANG - Blow process - The atmos' air is accelerated through the engine, the force required for this has an equal but opposite effect on the poor old motor shoving it in the opposite direction.
It is not a result of the jet exhaust pressure against the air or atmosphere.

If twas a rocket engine, with no surrounding 'atmosphere', the result would be the same, but then we could probably keep the handbrake on thus satisfying the requirement (if there ever was meant to be) of a stationary conveyor - due to non-rotating wheel - Ah but, was it 'rotational wheel' speed or wheel speed measured at the stub axle???
A driven car wheel generally travels at the speed of the axle - unless it has lost grip and 'spinning' - Of course a point on the tyre at the bottom rotating clockwise, vehicle moving left to right, will be moving in the vehicle direction at a slower speed than a point at the top of the same wheel....
More or less...

Balenza · 11 May 2008

Diyitall wrote

Yet again you are forgetting one small point.

You can stand the magical object on the belt and hook it up to your winch.

Start the belt up and the wheel will turn at exactly the same speed as the belt, to make any gain from its position on the belt, the wheels have to go faster than the belt.

All the time the speed of the wheels are the same as the belt, the object will not move.

What is so difficult to understand

Thier is nothing difficult to understand about what you have written here except the fact that the wheels cannot turn at the same speed as the belt.

Balenza · 11 May 2008

Diyitall wrote

Provided the wheels are the same speed as the belt it won't move.

Define speed ?.

doitall · 11 May 2008

Whether they can turn at the same speed is irrelevant, in the OPs post they DO

namsag · 11 May 2008

What happens if the guy forgets to turn the winch on

Balenza · 11 May 2008

doitall said:
Whether they can turn at the same speed is irrelevant, in the OPs post they DO

Whats the matter ?.
Question too difficult ?.

JohnD · 11 May 2008

doitall said:
Whether they can turn at the same speed is irrelevant, in the OPs post they DO

But the OP is wrong and this cannot occur so it is not possible to solve his question.

2scoops0406 · 11 May 2008

I agree with Balenza, it is frictionless so the wheels by definition cannot exert any force, therefore cannot rotate.

physics puzzle no.2

namsag

2scoops0406

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