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Homework Help: Help with dynamics

  1. Oct 11, 2005 #1
    can u ppl plz cheack if these answers are correct

    1 a 1500 kg car travling at 25m/s {n} comes to a stop in 5 s wat is the net force

    ans- 7500

    2. a boy aplies a horizantal forse of 45 n to a 10 kg trunk is the cofficient of friction between the boy and the floor is .35 detrimne accelaeration


    3 two children pull a 15 kg sled one pulls with force of 30 n {e} and the other pulls with 45n{s10w} calc accelaration

    ans 3.3

    4. a 4 kg cart(1) , a 2 kg cart(2) , and a 1 kg(3) cart are seccessivly joined with ropes the system is pulled with a 14 n force app lied to cart 1, calc tension in the rope between cart 1 and 2
    ans- 8 n
    if there is any mistakes can u plz help me correct it
  2. jcsd
  3. Nov 14, 2005 #2

    Yor answers for Parts 1 and 2 are numerically correct, but you should include the appropriate units in your final answer.

    As for Part 3, I do not really understand the symbols "{e} and {s10w}". Can you explain it to me?

    Finally, I think your answer to part 4 may be incorrect. In solving this problem, we first treat all 3 carts as 1 system, and then we apply Newton's 2nd Law to determine the acceleration of the system. Since the carts are connected by ropes, and assuming that the rope does not become slack, each cart will have the same acceleration. Then, we draw a free body diagram for the forces acting on cart 1, and a repeated application of Newton's 2nd Law should get us the final answer!
    (P.S I think your answer of 8N is the net force acting on cart 1, but not the value for the tension in the rope between carts 1 and 2)

    All the best!
  4. Nov 15, 2005 #3
    To help more with fourth wuestion do send the equations written by you.
    what are the signs in 3rd question. thesesquestions look similar andmuch easier than the ones i solve nowadays. so i think i might help you. if the vectors in the thirs question are in differant direction thenfixing an appropriate co-ordinate system would help.
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