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Elastic Collision of a ball and wire

  • Thread starter Quincy
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  • #1
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Homework Statement


An 10.0 kg ball, hanging from the ceiling by a light wire 125 cm long, is struck in an elastic collision by a 1.20 kg ball moving horizontally at 7.50 m/s just before the collision. Find the tension in the wire just after the collision.


Homework Equations


M1V1o + M2V1o = M1V2f + M2V2f

The Attempt at a Solution


(1.2 kg)(7.5 m/s) = (10 kg)(Vf)

Vf = 0.9 m/s

Fc = mV^2/R = (10 kg)(0.9^2)/(1.25 m) = 6.48 N

Fc = T - mg
6.48 = T - (10 kg)(9.8)

T = 104.48 N -- Book says it's incorrect, what am i doing wrong?
 
Last edited:

Answers and Replies

  • #2
tiny-tim
Science Advisor
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Hi Quincy! :smile:
An 10.0 kg ball, hanging from the ceiling by a light wire 125 cm long, is struck in an elastic collision by a 1.20 kg ball moving horizontally at 7.50 m/s just before the collision. Find the tension in the wire just after the collision.

why will the tension be different if the ball has a horizontal velocity?
Because although it has a purely horizontal velocity, it has a vertical acceleration. :wink:

Use Ftotal = ma. :smile:
 
  • #3
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Hi Quincy! :smile:


Because although it has a purely horizontal velocity, it has a vertical acceleration. :wink:

Use Ftotal = ma. :smile:
I realized that right after i posted the problem :P, i edited it now but the answer's still incorrect.
 
  • #4
tiny-tim
Science Advisor
Homework Helper
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(1.2 kg)(7.5 m/s) = (10 kg)(Vf)
Nooo … you've ignored the momentum of the small ball after the collision. :redface:

Try again, using conservation of both momentum and energy. :smile:
 

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