Question

Question in next comment!

Answer 1

must be a hell of a question

Answer 2

okay i have a current mudoled by the following function \(\Large \sf\color{blueviolet}{I(t)=5e^{-2t}sin(t)}\)
we need to approximate the current after t=0.7 seconds in amperes
this is was in the exam, i did the calculation in degrees
i got I=0.015 amperes. Problem is i realized that i did wrong
and it should be in radians

Answer 3

No just simple! i just need verification!

Answer 4

i was so darn angry after the test hehe
i was sure to get full credit! but i realized i didn't pay attention to this

Answer 5

@satellite73 what do you think

Answer 6

i have no idea what this is
sorry

Answer 7

hah lol

Answer 8

i do know that if you are using sine as a function, it is a function of numbers, not radians or degrees or dollars of euros of fahrenheit or celsius
as such it does correspond to a function of angles, but only if the angles are measured in radians

Answer 9

the current i got using radians is I=0.73 amperes

Answer 10

you wrote
\[\Large \sf\color{blueviolet}{I(t)=5e^{-2t}sin(t)}\]but \(t\)i s supposed to represent time right?

Answer 11

okay! well basically that's what i did!

Answer 12

yes t corresponds to time
in seconds

Answer 13

time is neither radians nor degrees, nor parsecs or milligrams

Answer 14

ooh i see
you had your calculator is "degree" mode right?

Answer 15

that is what im talking about^_^ you got me

Answer 16

oops

Answer 17

i think my answer was wrong comparing the two currents i got
should be set to radians mode hehe

Answer 18

prolly

Answer 19

Darn it all! hehe i was so confident to get this^_^

Answer 20

Well thanks

Answer 21

i hope im wrong lol

Answer 22

about this

Answer 23

@ganeshie8 what do you think

Answer 24

should to the result be under degree mode or radian mode
that is my curiosity

Answer 25

radian mode

Answer 26

question : how do you know \(t\) is in seconds and not hours/years ?

Answer 27

the question stated t=0.7 seconds

Answer 28

that is damped harmonic oscillation, though the argument of the sine function has been simplifed to just t (missing 2Pi f) and the time is almost always in seconds with this stuff because seconds are SI units

Answer 29

it said what the current would be after 0.7 seconds

Answer 30

would you assume \(t\) is in hours if it asks to compute current after 0.7 hours ? :)

Answer 31

you always assume t is in seconds if given no other information. the reason is because this equation is a form of commonly encountered equation, again, one of damped harmonic motion. This is commonly found in RLC circuits

Answer 32

do you say \(\omega t= 2\pi ft\) or \(\omega = 360ft\) ?
i think it depends actually, but radians/second is what we use in engineering,,, and it should be easy to figure out based on context

Answer 33

you will still need to convert to second like inky said

Answer 34

@ganeshie8 I am merely being practical. The units of equations are not always labelled, and when they are not, certain assumptions are usually made about them.

Answer 35

I agree with you on that, I am an engineer myself :) my question was to answer @xapproachesinfinity 's question on why we use radians

Answer 36

I haven't practiced circuit in a long time so i can't remember what this stuff is about hehe

Answer 37

strictly speaking, the question must specify \(t\) is in seconds and \(\omega\) is in radians/second so that the student is not confused. however nobody add that info because the question becomes unnecessarily lenghty and almost all the time students use correct units without even thinking.

Answer 38

the question didn't mention anything beside that t is in seconds
this was a precalc question not physics!

Answer 39

lazy professor :P

consider distance funciton :
\[d=5t\]


If I ask you to compute the distance travelled after 5 minutes, is it proper to assume that t is in minutes ? the actual units of function could be in seconds or hours, right ?

Answer 40

Agree with that!

Answer 41

to clear the ambiguity, you must ask me two questions back:
1) what are the units of time ?
2) what are the units of distance ? (or) what are units of speed ?(not shown using variable)

Answer 42

you cannot compute distance travelled in 5 minutes without knowing above contextual info ^^

Answer 43

I agree with that!

Answer 44

again, we should not complain too much haha! your professor is the boss and you will get use to ur professor and subject over time and care less about these petty stuff ;)

Answer 45

haha, correct! let's leave at that
will ask the prof later about it^_^
thanks guys

Answer 46

hmm , yeah before asking there is something maybe could help which is the unity of units lol (idk what its called in english ) what i mean is there is standerd unit that we get used to use them together (usually been mintioned in ut apendex txt book ) like :- (velocity )
km/h , ,mile /h , m /sec

Answer 47

well that won't help though hehe
cuz we know we should use seconds
SI unit for t is seconds
for the current I SI unit is ampere
=======
the test mentioned t in seconds so you have to stick with that
my question was about when evaluating t=0.7
should i do that under radian mode or degree mode
ganesh mentioned something about angular speed being in radian/second
don't if you need to use this fact or not
i think for this question you just need to evaluate the 0.7! the only issue here
is whether we have to use degree mode or radian mode in the calculator