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DLS Group Title

At the same instant that a 0.50-kg ball is dropped from 25 m above Earth, a second ball, with a mass of 0.25 kg, is thrown straight upward from Earth’s surface with an initial speed of 15 m/s. They move along nearby lines and pass without colliding. At the end of 2.0 s the velocity of the center of mass of the two-ball system is:

  • one year ago
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  1. mayankdevnani Group Title
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    options??

    • one year ago
  2. DLS Group Title
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    A. 11 m/s, down B. 11 m/s, up C. 15 m/s, down D. 15 m/s, up E. 20 m/s, down

    • one year ago
  3. DLS Group Title
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    V(a)=20m/s V(b)=-5m/s

    • one year ago
  4. mayankdevnani Group Title
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    Since this is multiple choice, lets use 10 m/s^2 as the acceleration due to gravity.

    • one year ago
  5. DLS Group Title
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    so 0.50*20+0.25*(-5)/0.75

    • one year ago
  6. mayankdevnani Group Title
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    The trick is to look at the momentum of the system after 2 seconds. So for the heavy ball, after two seconds, it has a velocity of -20 m/s.

    • one year ago
  7. DLS Group Title
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    10+1.25/0.75 (wil we have a minus sign or are we considering just the mag?

    • one year ago
  8. mayankdevnani Group Title
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    Thus it has a momentum of -10 kg*m/s.

    • one year ago
  9. DLS Group Title
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    u took downwards negative?

    • one year ago
  10. mayankdevnani Group Title
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    yaa, i took downwards negative. The light ball will have a velocity of -5 m/s (15 m/s going up minus 20 m/s due to gravity gives 5 m/s downward). So it has a momentum of -1.25 kg*m/s.

    • one year ago
  11. mayankdevnani Group Title
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    In both cases, the negative sign indicates the momentum is downward, and the sum is -11.25 kg*m/s.

    • one year ago
  12. mayankdevnani Group Title
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    Find the velocity of the system by dividing by the total mass (0.75 kg)?? then solve it and you get your answer.

    • one year ago
  13. DLS Group Title
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    i took downwards positive and upwards negative,im getting something different

    • one year ago
  14. mayankdevnani Group Title
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    no, always took downwards negative and upwards positive

    • one year ago
  15. DLS Group Title
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    v=0+10*2 v=20m/s downwards and v=15-20 v=-5m/s upwards

    • one year ago
  16. mayankdevnani Group Title
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    no!!!!

    • one year ago
  17. mayankdevnani Group Title
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    Find the velocity of the system by dividing by the total mass (0.75 kg) and you get 15 m/s down. so your answer is option C) 15 m/s up.

    • one year ago
  18. DLS Group Title
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    wait u messed up!!

    • one year ago
  19. mayankdevnani Group Title
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    no,, 15 m/s down.

    • one year ago
  20. DLS Group Title
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    im taking downwards negative and upwards positive so for the 0.25 kg ball, v=15+20=35? we are taking upwards positive right

    • one year ago
  21. mayankdevnani Group Title
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    right

    • one year ago
  22. DLS Group Title
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    0.25*35=8.75

    • one year ago
  23. DLS Group Title
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    -20+8.75

    • one year ago
  24. DLS Group Title
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    oh :o

    • one year ago
  25. DLS Group Title
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    -11.25/0.75=-15m/s

    • one year ago
  26. DLS Group Title
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    i see! :D

    • one year ago
  27. mayankdevnani Group Title
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    okk

    • one year ago
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