Question

Why are these two answers wrong?

Answer 1

second one:
must use this rule:
\[\frac{ dV}{ dt } = \frac{ dV }{ dv }\frac{ dv }{ dt }\]

Answer 2

Hmm what numbers would I plug in though? would the dvs cancel?

Answer 3

find the derivative, so,
(2.99*10^16)/r^2

which then is written as
(2.99*10^16)*r^-2

then take the derivative like this...
(2) (2.99*10^16)*r^-2
then this..
(2) (2.99*10^16)*r^-3
then convert it back to a fraction
(2) (2.99*10^16) / r^3

thus
5.98x10^16 / r^3
then plug in r

taking the derivative is needed because the phrase "rate of change" is used in the question.

Answer 4

For the second problem: V = -Blv ---- (1)
v = 8t + 9
Substiture v in equation (1)
Then find dV/dt

Answer 5

In first problem don't forget the negative sign when you find dF/dr.

Answer 6

DemolisionWolf why did you not do the derivative of the top? Also when I plugged in r I got
1.927237236e^-4

Answer 7

Ranga: 1=8t+9
-8=8t t=-1

Answer 8

No.
v = 8t + 9
V = -Blv = -Bl(8t + 9)
What is dV/dt = ?

Answer 9

so it would be -4.8(8t+9) and then would I distribute?

Answer 10

Yes, distribute and then find the derivative.

Answer 11

V=-38.4 ah thanks for help, do you know what went wrong with problem one?

Answer 12

Yes. First you have to find dF/dr when F(r) = (2.99 x 10^16)/r^2.
DemolisionWolf has done it above. I will just add a negative sign to the result.
Can you try finding dF/dr by yourself again?

Answer 13

Don't worry about the constant term initially. Just find derivative for 1/r^2 first.

Answer 14

F(r)=-5.98x10^16 / r^3

F(r)=1/2r?

Answer 15

so it would be flipped and -2r

Answer 16

OK, you got dF(r)/dr = -5.98x10^16 / r^3 which is correct.
Just plug in r = 6.77 x 10^6

Answer 17

hmm I got -1.927237236e^-4, maybe I should use e instead of x10

Answer 18

You got mostly correct. But the e should be 10.
The answer is -1.927237236 x 10^-4

Answer 19

I typed that in and it wants an exact answer so I x10^-4 and got -192723.724 but it still coming up as incorrect let me try again.

Answer 20

Try 0.00019272372

Answer 21

still no luck

Answer 22

Don't forget the negative sign

Answer 23

Does it say how many decimals in the answer or if the answer should be in scientific notation?

Answer 24

ahhh that got it lol, that weird why it did not take scientific notation, thanks a lot for the help!

Answer 25

Glad to help.