Question

can someone help me with number 7 and 10. I am lost

Answer 1

i know Total energy of satellite in orbit = -GMm/2r but when i solve for a I get a negative answer of -15632812 J

Answer 2

this is 7a

Answer 3

Regarding #10: Since the masses assumedly are not moving, the net external force on each is zero. Of course, if you're considering gravistational forces, Your answer may be different.

Answer 4

thats why it was confusing to me seemed like a trick question wouldnt it just be 0 or the gravitational constant perhaps

Answer 5

All bodies exert gravitational forces on other bodies. There's a standard formula for this type of force. Of course the forces involved are so small that they're essentially zero, which is not to say that they ARE zero.

Answer 6

fnet=G (m1m2)/r

Answer 7

i was thinking about that but idk

Answer 8

Haven't worked with this in years. Check, please, whether that r should be just r, or r^2. Also, I seem to remember that both g and G appear in the numerator. Check that out. Search for "gravitational forces."

Answer 9

http://prntscr.com/ac6ap5

Answer 10

this is what i found

Answer 11

im lost

Answer 12

would it be for number 10 like 4.1E-10?

Answer 13

Your formula is fine. Thx for looking it up. G is just a constant.
Two masses are indicated: m1 and m2.
The distance between two masses in question is d, so d^2 is the square of that.

Look for a value for G, the constant in your formula.

Try to ask leading questions, so that you can learn from what currently makes you feel lost.

Answer 14

For #7 :

\[PE = -\dfrac{mMG}{r}\]

\[KE = \dfrac{1}{2}mv^2\]

Answer 15

I have a question for you, when do circular orbits occur?

Answer 16

I think it safe to assume that the satellites move in essentially (if not perfectly) circular orbits around the earth, at least in a problem of this particular level of difficulty.

Answer 17

G is 6.67E-11. I plugged it in and got 4.1E-10 for 10

Answer 18

circular orbits occurr when a smaller object gets caught in the gravitational pull of another far more massive object

Answer 19

You can figure out the orbital velocity by using the fact that the satellite is in circular orbit. Therefore there must act a centripetal force changing the direction of satellite continuously, pulling it towards the earth

Answer 20

Please show all your work if you'd like feedback. If you merely share your answer in isolation, then it implies that you expect your helpers to do entire problems from scratch so as to tell you whether your result is correct or not. Not realistic.

Answer 21

Yeah, so when the gravitational force equals the centripetal force in the simplest sense, I guess you don't really need to know this considering the difficulty of your question :d hehe, what ganeshie gave should be good!

Answer 22

haha astro

Answer 23

so for total it is pe +ke

Answer 24

how do i determine the velocity for ke?

Answer 25

Which force is acting as centripetal force here ?

Answer 26

gravity?

Answer 27

i think the velocity of the satellite is 7907

Answer 28

m/s

Answer 29

Yes,

centripetal force = gravitational force

\[\dfrac{mMG}{r^2} = \dfrac{mv^2}{r}\]

just isolate \(v\)

Answer 30

doesnt velocity also equal v=sqrt((GM)/r)

Answer 31

which I could probably get by isolating that

Answer 32

v = 7907 m/s looks goo

Answer 33

I get a negative amount of energy when I plug in

Answer 34

-15632812 J

Answer 35

Maybe below expression for total energy of the satellite-earth system is simpler to use :

\[PE+KE = -\dfrac{mMG}{r}+\dfrac{1}{2}\dfrac{mMG}{r} = -\dfrac{1}{2}\dfrac{mMG}{r} \]

Answer 36

I got the same answer but positive

Answer 37

Negative value should make sense because we are defining 0 potential energy at infinity.

And the potential energy decreases as the distance between satellite and earth decreases

Answer 38

Oh ok

Answer 39

for b it would just be total energy of higher minus total energy of lower?

Answer 40

Yep

Answer 41

thanks :)

Answer 42

how do I go about 10

Answer 43

i was thinking just do Gm1m2/d^2

Answer 44

You need to add up the forces vectorially

Answer 45

maybe start by drawing a rough diagram

Answer 46

shoot just realized my answers are wrong for 7

Answer 47

i didnt factor in the height of the satellite when calculating

Answer 48

Happens haha!
\(r = \text{distance between satellite and center of earth}\)

Answer 49

yeah but its frustrating haha. After i recalculate ill make the diagram

Answer 50

take your time

Answer 51

ok new answer for higher sattelite is 2382142 J

Answer 52

with the 0 potential energy definite at infinity,
the total energy is always negative

Answer 53

yeah it was negative forgot to add the sign

Answer 54

my energy was higher at the lower orbit

Answer 55

it cannot be

Answer 56

remember

-8 < -2

Answer 57

oh duh

Answer 58

a large negative value is less than a small negative value

Answer 59

:(

Answer 60

my self esteem just died lmao

Answer 61

ok so how do i set up the diagram for 10

Answer 62

lol, maybe when free graph below functions :

f(x) = -mMG/r
g(x) = 1/2mv^2
h(x) = -1/2mMG/r

Answer 63

you will see something like below :

http://www.a-levelphysicstutor.com/images/fields/orb-PEKEgraph-01.jpg

Answer 64

Notice how kinetic energy is always positive

Answer 65

and how the potential energy and total energy are always negative

Answer 66

Also notice, all curves tend to 0 for large values of r

Answer 67

that makes more sense now

Answer 68

the negative had me confused for a bit

Answer 69

for #10
draw a square with four masses at four corners