Question

a ceiling fan is rotating at 0.96 rev/sec. when turned off, it slows uniformly to a stop in 2.4 min. How many revolutions does the fan make in this time? Can anyone help me with this question?

Answer 1

rev = 0.96 * 2.4 * 60

Answer 2

the answer is 69..if i calculate ur working steps, i get 138.24.

Answer 3

@syakamal are u here?

Answer 4

i think question is incomplete................ there should be -ve acceleration be given

Answer 5

really? -ve acceleration is when it rotates clockwise right?

Answer 6

when it turn-off........there is -ve acceleration which make it stop

Answer 7

okay..but then how the -ve and +ve signs affect the answer?

Answer 8

in your question you only mention initial speed and time not the acceleration by which it stops

Answer 9

okay but then how come the anser is 69, not 138? i'm so confused. Please help me

Answer 10

when there is -ve acceleration time of each revlution will inc by which it takes less revlution..that is the affect of -ve acceleration

Answer 11

@syakamal are u here?

Answer 12

i'm here..why?

Answer 13

read my reply and tell did you understand it or not

Answer 14

Alhamdulillah!..i got it..The question do says that it slows uniformly and then it stops

Answer 15

thanks

Answer 16

can u answer one more question, please?

Answer 17

Alhamdulillah???

Answer 18

sure

Answer 19

it means praise to Allah

Answer 20

If the angular acceleration considered to be constant, we can use \(\theta=\omega_0*t-\frac12 \alpha*t^2\)
I ended up with 69.2 rev
(I thought you both already got it :) Just trying to help.)

Answer 21

yeah..thanks imron

Answer 22

thankx @imron07

Answer 23

i have to go now but i will come soon

Answer 24

@uzumakhi @syakamal : did your browser convert my latext code into equation? Mine didn't.... I wonder what's the problem :/

Answer 25

uzumakhi, here is the question.. Using the result from part a (69.02), find the number of revolutions the fan must make for its speed to decrease from 0.96 rev/s to 0.48 rev/s.

Answer 26

omega^2=omega0^2-2*alpha*theta
omega=angular vel
omega0=initial angular vel
alpha=angular acceleration (found in first problem)

Answer 27

i am back............sorry i have to go to have lunch

Answer 28

its ok..sorry if i'm disturbing u

Answer 29

you are not disturbing me i love to solve this type of sums

Answer 30

initially i was saying the question is incomplete......so contact to your teacher and after that we will together solve it

Answer 31

ok

Answer 32

its better if you close the question and try another one

Answer 33

thanks for ur help