Trial HSC Questions - Help (1 Viewer)

[BrotherBread]

I think our teacher isn't teaching us adequately, that or this is a bogus trial HSC because I can't answer this question about Escape Velocity.

Describe the method Newton used that allowed him to show how the 'escape velocity' of earth could be calculated. (3mks, 9 lines)

I wasn't sure but I used his thought experiment of throwing rocks from a tower to establish the idea that at any given altitude there is avelocity that achieves a stable orbit, and then said that later this concept was used to calculate escape velocity. Is that about right?

Another one I am having trouble doing concerns the Mich-Mor exp

The exp by Mich-Mor won them a national prize in physics in 1888 'Not only for what they have established but for what they have unsettled.' With detail on the basis of the experiment, discuss what had been shown by the experiments and what been unsettled. (6mks 22 lines)

I know the experiment and all the rest of it, how it proved that light didn't require a medium etc, but I can't get the gist of what it wants to to say.

One calculation based question I am struggling with is

At launch a rocket and payload have a total mass of 4.8 x 10^5kg. The thrust produced by the rocket engines in the first second as the rocket begins to move is 1.43 x 10^7 N. The rocket was used to place a satellite of mass 820kg into orbit with an orbital velocity of 7.475 km/s.

a) calculate the average acceleration of the rocket during the first second of launch(2 mks, 3 lines)

b)providing in full detail, explain how orbital velocity can be used to calculate the altitude above earth of the satellite's circular orbit

I don't even know if that is in the syllabus. And I think that the whole lines are bogus too as in the HSC the lines are nowhere near as big as normal leaf lines.

Any help and or guidance would be much appreciated.

 

[ianc]

Describe the method Newton used that allowed him to show how the 'escape velocity' of earth could be calculated. (3mks, 9 lines)

I wasn't sure but I used his thought experiment of throwing rocks from a tower to establish the idea that at any given altitude there is avelocity that achieves a stable orbit, and then said that later this concept was used to calculate escape velocity. Is that about right?

Yes, this is the right thing to use for the question.....just say that if it is launched faster than the velocity which caused it to enter an orbit, the projectile will leave the earth entirely and thus this is the escape velocity.

Another one I am having trouble doing concerns the Mich-Mor exp

The exp by Mich-Mor won them a national prize in physics in 1888 'Not only for what they have established but for what they have unsettled.' With detail on the basis of the experiment, discuss what had been shown by the experiments and what been unsettled. (6mks 22 lines)

I know the experiment and all the rest of it, how it proved that light didn't require a medium etc, but I can't get the gist of what it wants to to say.

Okay the Michelson-Morley experiment didnt prove that light didnt require a medium. However it proved that there was no motion of the earth through the ether.

An attempt was made to explain the negative result by saying the earth carried the ether along with it, but it was implausible and easily disproved.

So the whole wave model of light was unsettled because the assumed medium was unable to be detected. Also, an idea which the Michelson-Morley experiment could not rule out was that the speed of light is constant in all directions - and obviously this is not a wave like property.

Hence, the Michelson-Morley experiment, despite its many criticisms such as not having accurate enough equipment, would have unsettled physicists because it showed that they do not understand something as fundamental as light.

At launch a rocket and payload have a total mass of 4.8 x 10^5kg. The thrust produced by the rocket engines in the first second as the rocket begins to move is 1.43 x 10^7 N. The rocket was used to place a satellite of mass 820kg into orbit with an orbital velocity of 7.475 km/s.

a) calculate the average acceleration of the rocket during the first second of launch(2 mks, 3 lines)

Okay, they give you the thrust of the rocket in the first second and also its mass, so you simply use:
F=ma
1.43 x 10⁷ = (4.8 x 10⁵) (a)
a = (1.43 x 10⁷) / (4.8 x 10⁵)
a = 29.79 ms^-1

b)providing in full detail, explain how orbital velocity can be used to calculate the altitude above earth of the satellite's circular orbit.

No, this question is wanting you to equate the formula for centripetal force with that of gravity (because in orbit the centripetal force is caused by the earth's gravity)

Hope all this helps!

Feel free to ask more questions if you're still unsure. Good luck with the HSC!!!

 

[jyu]

[/i]Okay, they give you the thrust of the rocket in the first second and also its mass, so you simply use:
F=ma
1.43 x 10⁷ = (4.8 x 10⁵) (a)
a = (1.43 x 10⁷) / (4.8 x 10⁵)
a = 29.79 ms^-1

The weight of the rocket (+payload) has to be accounted for:

1.43 x 10^7 - 4.8 x 10^5 X 9.8 = 4.8 x 10^5 a

a = 2.0 x 10^1 ms^(-2)

:wave:

 

[BrotherBread]

Thanks heaps guys, you have been a great help. I can't believe I missed the F=ma one, so damn obvious...

Thanks a bunch much appreciated.:wave: