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Homework Help: Mastering Physics 9.42

  1. Mar 12, 2005 #1
    Not sure of the number, but it is about a weather rocket that explodes.

    A 1500 kg weather rocket accelerates upward at 10\;{\rm m}/{\rm s}^{2} . It explodes 2.0 s after liftoff and breaks into two fragments, one twice as massive as the other. Photos reveal that the lighter fragment traveled straight up and reached a maximum height of 530 m.

    That is the problem.

    What was the speed of the heavier fragment just after the explosion?

    That is the question.

    I solved and got 20.96 m/s. It gives me this error:

    You are close. You may have made a rounding error or used the wrong number of significant figures.

    Help!!! What is the right answer?
  2. jcsd
  3. Mar 12, 2005 #2


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    Homework Helper

    How did u get that #...?How many sign.digits are u required to use...?

  4. Mar 12, 2005 #3
    Using the 10m/s^2 * 2s, i got the v_i to be 20 m/s, p_i then is 30000 kg*m/s.

    p_f is 1000*v_f_1 + 500*v_f_2

    Used v_f^2 = v_i^2 + 2*a*s on the smaller mass fragment. Used v_f = 0, a = -9.8, s given in problem. Solved for v_i. This v_i is the inital velocity of the fragment, aka its velocity at the end of the explosion.

    Set 30000 = 1000*v_f_1 + 500*v_f_2, using v_f_2 from dynamics equation work above. solved for v_f_1.

    EDIT: The system is evaluating my answer as 21.0, so i think my sig figs are right. Unless the server is broken, which could be the case.
  5. Mar 13, 2005 #4
    Anyone have any ideas?
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