That tower question (1 Viewer)

[xque]

omg i just said tower A mass would drop to the earth at an accelerated rate. I didn't say it would drop at an accelerated acceleration. AARRRRRRGGHHHHH.

 

[someth1ng]

Awesome question.

Definitely will discriminate the band 6 students from the band 5 students.

Probably discriminate even between band 6 students...

 

[OlliePOP95]

Tower B's mass has a velocity of geostationary satellites due to the Earths rotation, and Tower A only has velocity from the Earth's rotation around the Sun, which is negligible, therefore Tower B would remain in a geostationary orbit while tower A would return to Earth.

 

[jeffwu95]

killer question lol hopefully i got 2/4 (y)

 

[someth1ng]

Tower B's mass has a velocity of geostationary satellites due to the Earths rotation, and Tower A only has velocity from the Earth's rotation around the Sun, which is negligible, therefore Tower B would remain in a geostationary orbit while tower A would return to Earth.

For the bolded but, the first bit is good but the second bit is sorta wrong - it's not exactly, negligible. It's because there is not relative notion between it and the Earth.

 

[Zeroes]

best question I've seen in the HSC. hsc physics needs more shit like this rather than "impact of transistors"

This x100000000000

Still confused as to how B would stay in a geostationary orbit as some people are saying... wouldn't it need to have achieved orbital velocity relative to the earth to do that? If you look at Newton's explanation of escape velocity which includes orbital motion, a projectile has to be launched to stay in orbit, you can just toss the thing down... even though the earth is rotating the top of tower B is stationary with respect to the surface of the earth.

 

[Sweatyspuds]

The mass on the tower at the equator would fall straight down because it has the same angular momentum as the earth upon being dropped, so although it would fall in a parabolic arc the earth would spin at the same speed so it would still land near the bas of the tower.

 

[deswa1]

Don't think so. Mass A one was at a geostationary height, but it was on the vertical axis -- i.e. it wasn't orbiting, only rotating. It would thus plummet to the earth. However, Mass B was rotating with the tower, i.e. rotating with a period of 24h. So if the tower were to disappear, it would continue orbiting in geostat orbit.

This is what I got.

But that would assume that the initial velocity of Mass B is enough to sustain a geostationary orbit, right?

Mass is irrelavant- orbital velocity is independent of the mass of the thing in the orbit

 

[someth1ng]

The mass on the tower at the equator would fall straight down because it has the same angular momentum as the earth upon being dropped, so although it would fall in a parabolic arc the earth would spin at the same speed so it would still land near the bas of the tower.

It maintains its circular motion.

 

[erckle999]

How many marks do you think I could get if I correctly said that the mass from tower A would fall onto the north pole (as the north pole is on the axis of rotation) but did not realise that mass B has an initial horizontal velocity and thought it would just fall straight down to the earth somewhere on the equator as the earth spun around?

 

[deswa1]

How many marks do you think I could get if I correctly said that the mass from tower A would fall onto the north pole (as the north pole is on the axis of rotation) but did not realise that mass B has an initial horizontal velocity and thought it would just fall straight down to the earth somewhere on the equator as the earth spun around?

Depends on the marking scheme- its impossible to tell. One or two I'd imagine.

And I know this is sorta off topic but just quickly, what did you guys get for the solenoid and balance question? Did you put that the balance reading increases or decreases?

 

[Dedopcat]

ah crap I wrote about orbital velocity/ changing values of g/ something vaguely of newton's thought experiment? 1/4?

 

[gurgler]

i'm fairly sure that tower b will not go into geostationary orbit. if we imagine that the earth spun really slowly, even if it was at the height of geostationary orbit, it wouldn't suddenly gain enough velocity to go into orbit. the mass will just drop down to where it is, and to an outside observer it'll travel in a parabolic motion. the ball would only go into stationary orbit if somehow the earth's spin was just at the right amount that the velocity at the top of the tower was equal to the orbital velocity, and i really doubt its like that. just my take on the question

 

[Sweatyspuds]

Yea i just realised that rotational momentum of the earth would make it fly on a tangent but gravity acts as the centripetal force. I was thinking that because the tower rotates with the earth there was nothing keeping the mass up, but i forgot about the momentum

 

[someth1ng]

Depends on the marking scheme- its impossible to tell. One or two I'd imagine.

And I know this is sorta off topic but just quickly, what did you guys get for the solenoid and balance question? Did you put that the balance reading increases or decreases?

Balance decreases because the solenoid will produce a pole that attracts the magnet to oppose the change of flux.

 

[erckle999]

Depends on the marking scheme- its impossible to tell. One or two I'd imagine.

And I know this is sorta off topic but just quickly, what did you guys get for the solenoid and balance question? Did you put that the balance reading increases or decreases?

For the balance, as the solenoid moved away from the north pole (I think that was the one facing up) a south pole would have been set up to try and move the solenoid back toward the magnet (ie resisting the change in flux). Therefore the magnet on the scale would have been attracted to the south pole that was set up. Therefore less weight force, therefore reading would decrease (and go back up as the solenoid moved further and further away)

 

[erckle999]

Balance decreases because the solenoid will produce a pole that attracts the magnet to oppose the change of flux.

beat me to it...

 

[deswa1]

Balance decreases because the solenoid will produce a pole that attracts the magnet to oppose the change of flux.

Yay good

 

[jenslekman]

For the balance, as the solenoid moved away from the north pole (I think that was the one facing up) a south pole would have been set up to try and move the solenoid back toward the magnet (ie resisting the change in flux). Therefore the magnet on the scale would have been attracted to the south pole that was set up. Therefore less weight force, therefore reading would decrease (and go back up as the solenoid moved further and further away)

i thought about writing weight force but its really the net force? - i just wrote force just in case i get marked down =/

 

[erckle999]

i thought about writing weight force but its really the net force? - i just wrote force just in case i get marked down =/

You are right, in the exam I wrote something like: The magnetic attractive force counteracts the weight force leading to a lesser reading on the scale.