need help with questions (2 Viewers)

[greecke]

hey guys, i have a couple of questions i have done but the answers i got are not right but i dont know why. so...if anyone can do these and give the answer and why it is right, any help appreciated:

Two satellites orbit the earth, satellite A at 300km from earth and satellite B at 35800km. which is the most correct statement:
A) satellite B completes one orbit of earth in less time than A
B) A experiences greater centripetal force than B
C) B moves faster than A
D) A is likely to remain in a fixed position in the sky

Astronauts are more easily able to cope with an applicatoin of g;forces which results in the eyeballs undergoing relative motion towards the body rather than away from it. Which of the following combinations of positions are most desirable to acheive this effect?
A) Astronaut facing in direction of motion during launch and re-entry
B) Astronaut facing opposite to the direction of motion during launch and re-entry
C) Astronout facing in the direction of motion during launch and facing opposite to the direction of motion during re-entry
D) Astronaut facing opposite to the direction of motion during launch and facing in the direction of motion during re-entry

Any help greatly appreciated

 

[pravski]

Astronauts are more easily able to cope with an applicatoin of g;forces which results in the eyeballs undergoing relative motion towards the body rather than away from it. Which of the following combinations of positions are most desirable to acheive this effect?
A) Astronaut facing in direction of motion during launch and re-entry
B) Astronaut facing opposite to the direction of motion during launch and re-entry
C) Astronout facing in the direction of motion during launch and facing opposite to the direction of motion during re-entry
D) Astronaut facing opposite to the direction of motion during launch and facing in the direction of motion during re-entry

The naut has to be facing in direction of motion when going up, and when going down has to be facing down.

If he faces up when going up, the eyeballs have inertia so they get pushed into his head.
When going down the astronaut has to face down so his eyeballs move into their sockets even further because they have inertia.
So I guess that means the answer is A

 

[greecke]

thats what i got but the answers i was given said the answer is D

 

[Jago]

B and A .

 

[Haku]

no, the answer is B.

 

[jemsta]

isnt it that when your re-entering, you have to face down in relation to the direction your re-entering because if not, then wont your eyeballs be towards the back of your head due to the amount of g=forces acting on the astronaut?

 

[speed2]

these are from CSSA 05 right?
for question 1 the answer is C, because at launch the space craft is acc. up so that means their is a force towards the earth felt by the astronaut, hence eyeballs go in. coming back down the space craft is again acc. up (remember its slowing down) so the astronaut must face the same way as before but since he's moving towards the earth it would be opposite to the direction of motion.

 

[Xenocide]

speed2 is correct; the answer for the second mc is c) while the answer for the 1st mc is a). I am pretty sure if the answer for the 2nd one given is D it is a mistake.

 

[JumboKHS]

For satellite question the answer is B)
For the astronaut question the answer is C).

The satellite question is very simple, you can even work it out from method of elimination because the other answers are completely wrong. Satellite A, closer to earth experiences a greater centripetal force because in this system the centripetal force is gravity and we know that as distance is decreased then the gravitational force due to that mass increases.

----

For the astronaut question all you need to do is imagine the eyeballs floating in the spacecraft during its motion. As a result of inertia things tend to move in the opposite direction to acceleration. I.e. when you step on the accelerator in a car you are pushed back into the seat in opposite direction to the acceleration, and when you slam the breaks you are pushed forward, in the opposite direction to the acceleration.

On lift off the acceleration of the rocket is upwards. Thereforce due to inertia the eyeballs will tend to move in the opposite direction to the acceleration so they will move back down to the bottom of the spacecraft so to have the 'eyeballs-in' effect in this situation the astronaut needs to be facing upwards in the direction of the acceleration so the eyeballs move downwards into the sockets.

On re-entry the spacecraft once again is accelerating upwards! This is the only trick in the question, because the craft if slowing down the acceleration is in the opposite direction to the motion. So because the acceleration is upwards in this case as well the inertia of the eyeballs will make them go down, so to have the eyeball-in effect you need the astronaut facing upwards i.e. in the opposite direction of the acceleration.

 

[Xenocide]

sorry my bad, that was a typo JumboKHS is correct