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Draw an FBD of the system of A+B together. From this FBD you see that linear momentum is conserved for this system in the direction of motion. Use this to find the common speed of A and B once they stick together.
Let us know if you have questions on this.
9 comments:
The value that I am getting for the loss of energy is delta_E = 2422 ftlb, which is not correct according to the book. My method to find the answer is as follows:
delta_E = KE_final - KE_initial
KE_final = (1/2)(m_a+m_b)(v_final)^2
KE_inital = (1/2)(m_a)(v_a)^2 + (1/2)(m_b)(v_b)^2
I have made sure to convert all my units to feet and seconds. Please let me know if I have made any errors.
Did you convert from weight to mass properly? Other than that, your error seems small. Probably a simple math error forgetting a zero or a square.
Dale I'm having the exact same problem as you. I've triple checked and can't seem to get the answer in the book. I get 2422 everytime. Let me know if you figure out what we're doing wrong.
1st, Have to convert the mass. The 150.000 lb & 120.000 is weight, so need to be devided by 32.2 to get the "mass in lb".
2nd, have to convert the mi/hr to feet/second, because the answer is in ft-lb :)
i also get 2422 every time, maybe the book is wrong.
I know this is kind of late, but to get the answer in the book you have to use the exact v_2 (2.4 with the 4 repeating.) Then use a more exact g value like 32.174 and you'll get the book's answer.
I've tried a bunch of different ways to see how you came up with 2422ft-lb but I can't seem to do it. If you make sure everything is converted the right way and put the numbers into the calculator right, you should get 2226 ft-lb. Double check your numbers one more time to make sure they're all right.
I am trying to figure out whether or not that would even give you anything more than 0, as I set KE_final EQUAL to KE_initial to get the final velocity, which would imply that delta_E = 0.
Sorry, disregard my last post, I forgot that it's momentum that's conserved, not energy, so although I got a close answer, I did not calculate velocity for part A correctly.
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