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Homework Help: Velocity, IMA/AMA, circuits

  1. Jun 24, 2010 #1
    1. The problem statement, all variables and given/known data

    Need some help on basic Physics questions..... taking teh CSET (I'm a biology major) that involves a lil physics and i'm having brain farts... thanks...

    #1)I know that the area under v vs. t curve represents the object's displacement between a certain duration on time..... what is the area under a vs. t cute represent?

    #2)Car travels 20 km W, then 20 km S... What is magnitude of displacement?

    #3)2 vectors of magnitude 20 and 50 km are added. Which is the magnitude of their resultant?

    #4) Ramp at loading dock measures 6m long and 1m high. It has an efficiency of 2/3. How much effort force will be required to push a 60 N block of ice up the ramp?
    (I know efficiency=AMA/IMA and AMA=load/effort.....)

    #5) Block and tackle has an IMA=5 and AMA=4. If input work is 100J, how much work is lost in overcoming distance?
    (I know IMA=distance of effort/distance load and AMA=load/effort)

    #6) Student weighing 4540 N sits on a seesaw 0.60 m from fulcrum. How far from fulcrum on the other side should a child with a weight of 5000 N sit so seesaw is balanced?

    #7) Cube of wood with denisty=.780g/cm3 is 10.0 cm on each side. WHen cube is placed in water, what buoyant force acts on wood? density of water=1.00 g/cm3
    (I know Fb=density of fluid*V*g....)

    #8)Mass of iron weighs 1000 N in air but only 872N when immersed in a fluid. What buoyant force does this fluid exert on the iron?

    #9) If the phenomenon of atmospheric refraction did not occur, how mught the apparent time of sunrise and sunset be affected? Answer is sunrise later and sunset earlier.... Why?

    #10) When placed near the N pole of a permanent magnet, the pointed end of a sweing needle will be.......attracted is the right answer. Why? I thiugh it would be repelled.

    #11) A simple circuit consists of only 2 identical bulbs. The current in the circuit is 0.25 amps. The sum of the voltages across the bulbs is 24 V. The resistance of a single bulb light would be a) 96 ohms b)48 ohms c) 24 ohms d) 12 ohms

    2. Relevant equations

    Above ^^^

    3. The attempt at a solution
    Above ^^^
  2. jcsd
  3. Jun 25, 2010 #2
    #1. x is the area under the curve of v vs. t because v = dx/dt. What's the definition of acceleration?

    #2. They form a right triangle, so use the Pythagorean theorem.

    #3. Impossible to say. Not enough information. Vector addition takes into account both magnitude and direction. (see #2)

    #4. You need to calculate the IMA. Using the efficiency you will get the AMA. Use that to answer the question.

    #5. You know input = 100 J. Ideally the output would be what? (Use IMA) But what is it really? (Use AMA). The amount lost is the difference between these numbers.

    #6. The torques around the fulcrum must balance.

    #7. The wood floats, so the V is only the volume of the block underwater. But a quicker way is to note that because the wood is floating (equilibrium) the bouyant force must be exactly equal to the weight of the block.

    #8. The bouyant force is precisely why the weight is less.

    #9. The light bends as it enters the atmosphere (Snell's law). Think about the geometry of the problem. When you see the sun setting is it actually above or below the horizon?

    #10. The sewing needle has no inherent magnetic field. But bringing it close to the magnet induces one. All the atoms in the sewing needle line up in response. Do you think they will line up with their north or south poles toward the magnet? Remember opposite poles attract, similar poles repel. Once they line up, will the needle be pulled toward or pushed away from the magnet?

    #11. What is the total resistance of the circuit? (Hint: use Ohm's law). Since the bulbs are identical (and presumably in series), each bulb will be half the total.
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