anonymous one year ago It takes 0.225 seconds/revolution for a body of mass of 25 grams to rotate a circle with a radius of 15 cm. What is the centripetal force acting on that body?

1. welshfella

force = m w r^2 F is in Newtons . mass in kgs and r in meters w = the angular velocity in radians / sec you can work this out from the given speed in revs / sec.

2. anonymous

how can I convert seconds/revolution to radians/sec?

3. welshfella

1 rev = 2 pi radians it travels 2 pi radians in 0.225 secs so in 1 second it travels 2 pi / 0.225 radians

4. welshfella

w = 8.89 pi rads/sec

5. anonymous

5x10^(-3) ?

6. welshfella

now you need to convert 25 gms to kgs and 15 cms to meters.

7. welshfella

what is 5x10^-3 ?

8. anonymous

the answer for the centripetal force?

9. welshfella

hmm..

10. welshfella

not quite - you need to multiply that by pi

11. anonymous

sorry i forgot to put pi, is it 0.0157?

12. welshfella

yes thats in newtons

13. welshfella

you can write it as 1.57 * 10^-2 N

14. anonymous

the answer is not in the choices :(

15. anonymous

i know other formulas maybe we can try that :)

16. welshfella

oh - maybe i've gone wrong somewhere - its been a while since i did these what are the choices?

17. anonymous

$T = 2\pi(r) \over v$

18. anonymous

0.731 N, 749.47 N, 187.368 dynes, 2,924 N

19. Jhannybean

Isn't centripetal force $\sf F_c = \frac{ mv^2}{r}$

20. welshfella

yes where v = linear velocity

21. anonymous

yes @Jhannybean :)

22. Jhannybean

since centripetal acceleration = $$\sf a_c = \dfrac{v^2}{r}$$

23. Jhannybean

cool, I still remember $$\checkmark$$ haha

24. welshfella

yea my memory has failed me here I should have checked

25. welshfella

i was too confident lol!

26. anonymous

$T = \frac{ (2\pi(r)) }{ v }$

27. anonymous

|dw:1438464437672:dw|

28. anonymous

is it correct?

29. welshfella

my original equation should have been m w^2 r so F = 0.025 * (8.89pi)^2 * 0.15

30. anonymous

oh it's 2.924 thank you :D

31. welshfella

= 2.925 N

32. anonymous

Can you help me with another problem ? :)

33. welshfella

2.924

34. welshfella

well i only have 10 minutes but see what i can do

35. anonymous

thank you :)