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Free Fall

 
 
fdrhs
 
Reply Sun 17 Jul, 2005 08:15 pm
A ball with a mass of 0.5kg is dropped from a height of 190cm. The ball is in flight for 5 sec, with gravity acting on it. We can assume that the ball will hit the ground and bounce back to half the initial height. Given this information determine:

a) How long will it take for the ball to come to rest?

b) How fast will the ball be traveling on the intial drop?
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Type: Discussion • Score: 1 • Views: 638 • Replies: 7
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markr
 
  1  
Reply Sun 17 Jul, 2005 08:44 pm
What do you mean by "the ball is in flight for 5 sec?" Is that the total time bouncing? Under normal conditions, the ball will reach the ground in well under 5 seconds?

If the ball always rebounds to half the previous height, then theoretically, it never comes to rest. It will, however, travel a finite distance.

The ball is accelerating after it is dropped. At what point do you want the speed?
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fdrhs
 
  1  
Reply Mon 18 Jul, 2005 05:29 am
ok
I don't know what the question is asking for; it was written by my teacher.
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alex-vcn
 
  1  
Reply Fri 22 Jul, 2005 06:34 am
i can help you.im not a american,so i might not say the words clear enough.first,the air is acting on it to slow it down,Q=k*l(l represent the length the ball travels in the air) second,the total energy the ball has is E=mgh(h the height),and the time it comes to a rest is the moment all the E is translated into heat.E=Q does it make any sense
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Brandon9000
 
  1  
Reply Fri 22 Jul, 2005 09:03 am
An object dropped from 190 cm with negligible air friction will fall for the following amount of time.

s = (1/2)gt^2

(2s/g) = t^2

t = SQRT(2s/g)

g = 9.8 m/s^2 * 100 cm/m = 980 cm/s^2

t = SQRT(2(190 cm)/980 cm/s^2) = SQRT(380/980 s^2)
= SQRT(0.388 s^2)
= 0.6227 sec.

This, not 5 seconds, is the amount of time that it will take the ball to reach the ground. I am not sure what this question means.

When the ball strikes the ground, its speed will be 0.6227 sec(980 cm/s^2) = 610 cm/s.
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fdrhs
 
  1  
Reply Fri 22 Jul, 2005 03:04 pm
hey
Thank you very much.
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Brandon9000
 
  1  
Reply Fri 22 Jul, 2005 11:09 pm
Sorry, I caught an arithmetic error. 9.8 * 100 = 980 not 9800. Hope the correction isn't too late.
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fdrhs
 
  1  
Reply Sat 23 Jul, 2005 10:00 am
hey
No it isn't too late.

Thanks
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