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Homework Help: A force question

  1. Mar 12, 2007 #1
    1. The problem statement, all variables and given/known data

    Car A is towing car B. Both cars have the same mass ma = mb = 1000 kg. Car A has four-wheel drive, and the static coefficient of friction between its tires and the road is µs = 1.00 Neglect any friction force acting on car B. Car A is accelerating at 1m/s/s. Calculate the tension in the horizontal rope connecting the cars.

    2. Relevant equations:
    F = ma
    and Friction = W. coefficient of friction

    3. The attempt at a solution

    So, First I found the net force that is being applied on the car B, that equals to 1000 x 1 = 1000 N. And so Tension = 1000 N

    I am wondering if this is correct? I am confused since I have ignored many other given information
  2. jcsd
  3. Mar 12, 2007 #2

    Doc Al

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    Staff: Mentor

    You are correct.
  4. Mar 12, 2007 #3
    As you get better at solving physics problems, you can gauge your skills based how easily you can identify exactly what information you need to get the answer. This skill makes labs and experiments much easier, because you know from the start precisely what you need to finish.

    In this case, that means realizing that much of the given information is irrelevant to the problem.

    Before you fall into the trap of "but I didn't use this bit of information!!!" remember that a right answer is a right answer, regardless of how much other material the problem throws at you.
  5. Mar 12, 2007 #4
    First of all Weight x coeff. Friction, is right, but the weight ain't 1000Kg !!! it's mass x gravity remember ?? Btw if you draw a Free Body Diagram for your system u'll realize that u really misused the information given to you, for example not all the force exerted by car A is going to the rope and to car B, some of it is lost, u know where?. Draw a F.B.D and suddenly you'll see what i mean.
  6. Mar 13, 2007 #5

    Doc Al

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    Staff: Mentor

    Nonsense! harmeet_angel has solved the problem correctly and used the given information properly. For the specific question asked--finding the tension in the tow rope--and the information given, the friction force exerted on car A is irrelevant.

    By the way, [itex]\mu N = \mu mg[/itex] gives the maximum value of static friction. If you were asked to find the amount of static friction pulling car A, you would not just plug the numbers into that formula. Instead, you would need to analyze the forces on car A and apply Newton's 2nd law--just like the OP did for car B.
  7. Mar 13, 2007 #6
    ok wait i didn't pay attention that the acceleration is the force pulling after friction has been taken into account.sorry my bad
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