## anonymous 5 years ago A building is being knocked down with a wrecking ball, which is a big metal sphere that swings on a 12-m-long cable. You are (unwisely!) standing directly beneath the point from which the wrecking ball is hung when you notice that the ball has just been released and is swinging directly toward you. How much time do you have to move out of the way?

1. anonymous

is that all the information you have?

2. anonymous

unfortunately

3. anonymous

i know that $T= 2pi sqrt{m/k}$

4. anonymous

$T=2\pi \sqrt{m/k}$

5. anonymous

so, $T = 2\pi \sqrt{L/g}$ where L = Lenght g = gravity

6. anonymous

T- period?

7. anonymous

T- period in seconds i mean?

8. anonymous

yes, because you know that gravity is in m/s^2 so, period will be measured in seconds. You know the cable is 12m long and gravity is 9.81 solve for T (period) $2\pi \sqrt{12/9.81} = 6.94922$

9. anonymous

ok cool i got 6.95 as well

10. anonymous

but, The release through the first vertical point is ¼ of the total cycle, so you have ¼ of the period to get out of the way. $6.95 * (1/4) = ?$

11. anonymous

but that is in hertz correct?

12. anonymous

period is in seconds i believe

13. anonymous

ah ok. i ended up with 1.7 seconds

14. anonymous

sounds right to me.

15. anonymous

im still a little confused as to why we multiplied by 1/4

16. anonymous

Period is the time that the ball takes to complete one cycle, as you are standing right beneath the ball (first vertical point) that is 1/4 of the cycle

17. anonymous

ah ok

18. anonymous

thanks! :)

19. anonymous

np (: