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Homework Help: Help with problems General physics

  1. Nov 6, 2006 #1
    help with problems!!!General physics


    I really need help with my physics test. Its a home test! Can anyone please help me.:smile:

    Problem 1:

    A Ferris wheel has radius 5.o m and makes one revolution in 8 seconds. A person weighing 670 N is sitting on one of the benches attached at the rim of the wheel. What is the apparent weight (that the normal force exerted on her by the bench) of the person as she passes through the highest point of her motion???????

    Answer: i got 723.6 N, can it be right?

    Problem 2:

    An 8.0 kg block is released from rest, v1 = 0 m/s, on a rough incline, which has an angle of 40 from the horizontal. The block moves a distance of 1.6 m down the incline, in a time interval of 0.80 s, and acquires a velocity of v2 = 4.0 m/s.

    The average rate at which work done by the weight is closest to...

    the Answer is +80j, but how do you get it?

    -----------------------------------------------------------------------Problem 3:
    Two objects, one of mass m, other of mass 2 m, are dropped from the top of a building. When they bit the ground:
    a) both will have the same kinetic energy
    b)the heavier one will have twice the kinetic energy of the lighter one
    c)the heavier one will have 4 times the kinetic energy of the lighter one
    d)the heavier onewill have half the kinetic energy of the lighter one.
    e)the heavier one will have one fourth the kinetic energy of the lighter one.
    Problem 4:
    Which of the following is an accurate statement?
    A) Kinetic Energy is always positive
    B) poptential energy is always positive
    C) Total energy is always positive
    D) None of these is true
    E) More than one of these is true

    // I know that kinetic energy is always positive, potential ? no, it can change, total? is it always constant?

  2. jcsd
  3. Nov 6, 2006 #2
    A is incorrect. You need to show some work where someone can show you where you are wrong.
  4. Nov 6, 2006 #3
    Hi kksyu, welcome.

    Gosh, I'm not sure if we are supposed to help with tests. This is a great place, though. If you come here with homework, and show people you are really trying, you will really be able to improve your physics. It has helped me so much.

    Here are some hints, I don't want you to think we are not friendly here.

    For problem 1, this is the same as would happen in an elevator. I'm sure you've seen that problem, with an elevator and a scale, and how it changes when you accelerate up and when you accelerate down. Think about that, and what direction your acceleration is at that point in your ferris wheel ride.

    For your second problem, well, you just need to think about what force is doing the work, and what direction that work is actually being done on. (Hint: It might not be the same as the direction of the motion.)

    I think your other questions can be answered with just some extra thinking, like about what equations are actually used in these situations, that sort of thing.

    Physics is such a great subject. Hope to see you here some more.

  5. Nov 6, 2006 #4
    For number 2 use the formula m*g*sin(x)*d.
    I got 82joules which is very close to the answer you gave.

    For number 3 the answer is a. The objects are dropped from the SAME HEIGHT and GRAVITY PULLS EQUALLY on all objects, so they will both have the same kinetic energy.

    For 4 I believe the answer is e. I don't believe an object can every have negative energy of any type. An object can have zero potential energy (if it's not elevated), but I don't think energy can ever be negative.
  6. Nov 6, 2006 #5
    Hi Grover,

    Please don't just give the answers. Anyway, your answer to 3 needs a bit more work, I think.

  7. Nov 6, 2006 #6
    For problem 4, everything is based on origin and positive direction choice
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