Some physics questions from MC dot point. (1 Viewer)

[PROFESSOROAK]

Hey guys, just some questiosn which i don't quite understand from the space topic of the Multiple choice Dot point textbook, was hoping to get some answers and explanations.

2.14.8

Two satellites, X mass 2000kg and Y mass 3000kg, are placed into orbits above Mars. The altitude of these orbits is two and three times the radius of Mars respectively. What is the ratio of their orbital speeds?

a) X:Y = 1:1
b) X:Y = 1:3
c) X:Y = 2:3
d) X:Y = 3:4

Answer is D, Don't understand why it would be 3:4, wouldn't it be 2:3??

2.15.5

Two plantes, X and Y orbit the same star as shown. Planet X completes one orbit around the star in time T. The radii of the orbits are in the ratio of 1:4. How many orbits does planet Y make in time T.

a) 1/8
b) 1/4
c) 1/2
d) 8

Don't understand how to approach this question.

2.15.6

Kepler's law of periods, summarised in the equation T^2 = kR^3, shows the relationship between the orbital period and radius of a planet orbiting a star. Which of the following would result in a change in the value of the constant, k?

a) A planet of different mass orbiting the same star.
b) A planet of greater orbital radius.
c) A planet of greater orbital period.
d) An identical planet orbiting a different star.

Ok, this one I just completely don't understand, don't know what the question is asking and wtf is T^2 = kR^3.

2.16.3

Why is a satellite in a LEO more likely to suffer orbital decay than a satellite in a geostationary orbit?

a) The LEO satellite is moving faster.
b) The LEO satellite is in denser air.
c) The LEO satellite has stronger gravitational force acting on it.
d) The LEO satellite satellite is moving more slowly.

I cancelled out d instantly because a LEO would be travelling more faster, and then C because the gravitational force would not start to affect unless the craft started to slow down right? Not quite sure, and also A I thought was right because the faster it moves, the more air friction it has so it drags it down? or something?

Thanks guys.

 

[khorne]

2.16.3:
Wouldn't it b B, since the denser air means more collisions/energy lost in friction?

2.15.6 keplar's law is t^2/r^3 = K (as GM/4pi^2) = constant for one planet.
so t^2 = Kr^3

therefore, to change the constant, M needs to increase, i.e a different star (with larger mass).

 

[kickass91]

2.14.8:
the orbital speed is sqroot (GM/r )
radius of the orbit of satellite 1 is 3 x the radius of mars (orbital radius =altitude + radius of the planet)
radius of the orbit of satellite 2 is 4 x the radius of mars (orbital radius = altitude + radius of the planet)

in fact, all of the answers are incorrect. the correct answer should be sqroot (4/3) i.e. 2/ root 3

2.15.5 :
kepler's law is r^3/ t^2 = r^3/ t^2
radius of y is 4 times the radius of x. therefore the period of y is also larger than the period of x
the answer is 1: 8
2.15.6
the constant k is 4pi^2/GM
u get this by deriving kepler's law when you equate the gravitational force to the centripetal force.
the only variable that changes is M, the mass of the star. hence the answer is D.

2.16.3 is B

orbital decay occurs because the LEO is in the upper part of the earth's atmosphere: so there's air friction.