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Urgent Help: An old handout

  1. Jun 1, 2007 #1
    1. I have to study for a test. To prepare to study, I decided to look around in my bookshelf for textbooks and to my surprise, found an old handout. I've typed out the questions and my response (answer) to those questions as itactalized. Please feel free to correct/help me :)

    PS: Ignore grammatical erros as I've typed it out in a hurry after finding it.



    2. The attempt at a solution:

    SECTION A- Please tell me which is corect/incorrect and please sugest/help me to correct my wrongs.
    1. A car is traveling on a level road. The driver has to stop quickly. Which of the following has the greatest effect on the stopping distance
    a. The kinetic energy of the car
    b. The potential energy of the car
    c. The straightness of the road
    d. How far the driver can see

    2. Which of the following depends on the atmosphere exerting a pressure
    a. A ball falling from the ground
    b. Drinking through a straw
    c. The spray from a can of cola
    d. Bath water emptying down a plug hole

    3. A ball attached to a string is whirled round at a constant speed in a horizontal circle. Is it true to say that
    a. The velocity is constant
    b. They are no forces acting on the body
    c. The motion is accelerated
    d. If the string breaks the ball drops vertically downwards

    4. If an object has kinetic energy, then it must also have
    a. Acceleration
    b. Force
    c. Momentum
    d. None of the above

    5. Two forces of magnitude 8N and 6N act on the same body at right angles to each other. The magnitude of the resultant of the force is
    a. 7N
    b. 10N
    c. 14N
    d. 48N

    6. A wire is stretched by a load to a point beyond its elastic limit. It follows that
    a. The wire will break if the load is increased any further
    b. If the load is removed the wire will resume its original length
    c. The extension will no longer be proportional to the load
    d. The wire cannot be extended any further if the load is increased

    7. A rock of mass 2kg falls 125m form a cliff top into the sea. Its momentum just before it hits the water is
    a. 20 kg m/s
    b. 50 kg m/sc. 100 kg m/s
    d. 200 kg m/s

    8. As a brick falls to the ground, it
    a. Loses potential energy and gains kinetic energy
    b. Loses kinetic energy and gains potential energy
    c. Gains both kinetic and potential energy
    d. Loses both kinetic and potential energy

    9. A mass M moving in a straight line with velocity v1 collides with a stationary mass m, and sticks to it. They continue to move in the same straight line with velocity v2. The equation from which the correct value of v2 may be obtained is
    a. Mv1 = mv2
    b. Mv1 = (M+m)v2
    c. ½ Mv12 = ½ mv22
    d. ½ MV12 = 1/2mv22

    10. A small marble of mass 10g is dropped form a height above a floor. After striking the floor, the marble rebounds to a height of 1m above the floor. The kinetic energy of the marble just after striking the floor is
    a. 0.02J
    b. 0.1J
    c. 0.2J
    d. 20J

    11. An electric drill fitted with a blunt bit is used in an unsuccessful attempt to drill a hole through a steel plate. The energy changes involved are best summarized by
    a. electrical  kinetic  heat/internal energy
    b. electrical  heat/internal  potential
    c. kinetic  electrical  potential
    d. kinetic  potential  heat internal

    12. The relationship between the volume and the pressure of a fixed mass of gas at constant temperature is called
    a. The kinetic theory
    b. Boyle’s Law
    c. Charles’ Law
    d. Pressure Law

    13. Which of the following statements about temperature is not true
    a. It represents the amount of heat contained in a body
    b. It is a measure of the degree of hotness or coldness in a body
    c. It is a property which determines the direction of heat flow in a body
    d. It measure the average kinetic energy of the particles of which matter is composed

    14. Which of the following scientists provided quantitative evidence for the law of conservation of energy
    a. Einstein
    b. Joule
    c. Newton
    d. Rumford

    15. A detector of thermal energy is placed an equal distance in turn form each of the four faces of a hollow metal cube full of water. the reading on the detector is the greatest when the detector is turned to the face which is
    a. painted silver
    b. painted shiny white
    c. painted dull black
    d. highly polished

    16. When illuminated smoke is viewed through a microscope, small bright specs can be seen moving in a jerky haphazard manner. These specks are
    a. atoms
    b. molecules
    c. smoke particles
    d. light particles

    17. Which of the following is not implied by the kinetic theory?
    a. The internal energy of a gas depends only on the gas temperature
    b. The pressure of a gas is caused by the gas molecules bombarding the containing surfaces
    c. The volume of the particles is negligible
    d. They are strong intermolecular forces between two molecules in a gas

    18. According the kinetic theory, what is the pressure of an ideal gas at absolute zero
    a. 1atm
    b. 760mmHg
    c. 101.3 kPa
    d. 0 mmHg

    19. Heat is transferred from the sun by
    a. Conduction
    b. Convection
    c. Radiation
    d. All of the above

    20. A 0.460Kilowatt water heater is used to boil water. Assuming no thermal energy loss, what mass of steam will it produce in 10minutes. The Specific latent heat of vaporization of water is 2300000J/kg
    a. 105800000000J
    b. 6348000000000J I THINK THIS WAS AN ERROR, A ‘0’ IS SUPPOSED TO BE REMOVED?
    c. 6348000000J
    d. 105800000J

    21. Geiger and Marsden were student of who?
    a. Thompson
    b. Rutherford
    c. Bohr
    d. Dalton

    22. Which of the following would be true of the Geiger Marsden experiment – (I) it established that an atom has a positively charged nucleus, (II) it demonstrated that alpha particles are positively charged, (III) it shows that alpha particles were never deflected
    a. I only
    b. I and II only
    c. II and III only
    d. I II and III

    23. Which of the following statements about eh expression E = mc2 is true? (I) it defines the maximum energy light can have, (II) it represents the fact that mass can be converted into energy, (III) it represents one of the major achievements of Rutherford
    a. II only
    b. I and II only
    c. II and III only
    d. I, II and III

    24. Which of the following may be used to define the term half-life. (I) it is half the time required by a nucleus to decay, (II) it is the time for half the nuclei of a sample to decay, (III)it is the time for an activity of any random process to fall to one half its original value>.
    a. I only
    b. I and II only
    c. II and III only
    d. I, II and III only

    25. Which of the three types of radiation carry’s an electric charge
    a. alpha and gamma
    b. Beta
    c. Alpha and beta
    d. Beta and gamma

    26. An alpha particle is
    a. A proton
    b. A helium atom
    c. A helium nucleus
    d. An electron

    27. Which of the following uses radioactive cobalt – 60
    a. Tracers
    b. Radiotherapy
    c. Carbon Dating
    d. The Dating of Rocks

    28. Which of the following isotopes of Carbon is used in Carbon dating
    a. 147C
    b. 146C
    c. 126C NOT SURE WHICH ONE, IF ANY AT ALL! PLEASE HELP
    d. 127C

    29. Which of the following contributes the most to Background radiation
    a. Radon gas from ground COMPLETE GUESS, NOT SURE
    b. Buildings
    c. X-Rays
    d. Nuclear Waste

    30. Which of the following is the most dangerous to living organisms
    a. alpha
    b. beta
    c. gamma
    d. they are all equally dangerous





    SECTION B- please tell me if i'm correct/incorrect and also feel free to help/suggest for my wrongs.
    1. In a vacuum, a feather will not fall at the same rate as a stone FALSE
    2. Free Fall and The Pendulum Swing are not the only methods that can be used to determine the value of gravity..FALSE
    3. The equation s = ½ (v + u)t is not an accurate equationTRUE
    4. If a body is project horizontally off of a cliff the horizontal distance is equal to the distance it would have traveled if on a straight planeFALSE, NOT SURE
    5. The equation E=mc2 invalidates the law of conservation of massFALSE
    6. A stiletto heel shoe will cause more damage to a polished floor than a flat heelTRUE? NOT SURE, LOL.
    7. The potential energy and 1/3 height is equal to the kinetic energy at 4/6 heightFALSE..EH?
    8. The mercury in glass thermometer can be used to measure bother very high and low temperaturesFALSE..NOT SURE
    9. The Higher the specific heat capacity of a substance, the longer it will take to change its temperatureTRUE...EH?
    10. Both evaporation and boiling of a liquid involves a change in temperatureFALSE

    Even though I might not have said that I am not sure, please tell me which questions are correct/incorrect. Thanks alot:smile:
     
    Last edited: Jun 1, 2007
  2. jcsd
  3. Jun 1, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    1 - 10

    OK.

    No. I assume that should read "A ball falling to the ground". In any case, would a ball fall on the Moon?

    No. How does velocity differ from speed?

    OK

    No. How did you calculate this?

    OK

    No. What's the speed?

    Good

    Good

    No. Hint: Consider potential energy.
     
  4. Jun 1, 2007 #3

    Doc Al

    User Avatar

    Staff: Mentor

    11 - 20

    OK

    OK

    No. Note it asks for what is not true.

    No. Consider the standard unit of energy!

    OK

    OK

    OK

    OK

    OK

    ? These answers are Joules, not mass.
     
  5. Jun 1, 2007 #4
    Corrections:

    1)The spray from a can of soda.

    2)There are no forces acting on it.

    3)10 N. I realized my mistake, careless one by the way!

    4)7. A rock of mass 2kg falls 125m form a cliff top into the sea. Its momentum just before it hits the water is
    a. 20 kg m/s
    b. 50 kg m/s
    c. 100 kg m/s
    d. 200 kg m/s

    I still am getting 50 kg m/s... I used s=ut + 1/2at^2 where:
    s=125 m
    u=0
    t=?
    a=10
    t^2=?

    I think I did the equation wrong :(

    5) 10. A small marble of mass 10g is dropped form a height above a floor. After striking the floor, the marble rebounds to a height of 1m above the floor. The kinetic energy of the marble just after striking the floor is
    a. 0.02J
    b. 0.1J
    c. 0.2J
    d. 20J

    Still don't know what to do :(

    6)Joule

    7)The amount of heat in the body? Still skeptical.

    8)20. A 0.460Kilowatt water heater is used to boil water. Assuming no thermal energy loss, what mass of steam will it produce in 10minutes. The Specific latent heat of vaporization of water is 2300000J/kg
    a. 105800000000J
    b. 6348000000000J I THINK THIS WAS AN ERROR, A ‘0’ IS SUPPOSED TO BE REMOVED?
    c. 6348000000J
    d. 105800000J

    The answers are indeed not in mass, but I figured it was a typo and it was supposed to be the energy? I don't know...
     
  6. Jun 1, 2007 #5

    Doc Al

    User Avatar

    Staff: Mentor

    OK

    OK

    No. What determines the energy of light?

    No. A particular nucleus doesn't have a set time to decay.

    OK

    OK

    No. Look up the uses of cobalt 60.

    ? I don't understand these answers. Carbon dating uses Carbon 14.

    Hmmm... good question. Of the choices given, I would pick buildings. But you better look it up.

    Sounds right. Gamma radiation penetrates, but alpha particles would not be good if you eat a source of them.
     
  7. Jun 1, 2007 #6

    Doc Al

    User Avatar

    Staff: Mentor

    Don't change the question numbers!:yuck:

    Both incorrect.

    OK.

    You'll need another kinematic equation. Look them up!

    Several ways to go: (1) Use kinematics to find the initial speed of the marble as it leaves the floor, or (2) Consider the energy it has when it leaves the floor.

    Of course!

    Consider a 1 gram object and a 1 kilogram object at the same temp--do they have the same "heat" (internal energy)?

    Beats me what they want here.
     
  8. Jun 2, 2007 #7
    1. In a vacuum, a feather will not fall at the same rate as a stone FALSE
    2. Free Fall and The Pendulum Swing are not the only methods that can be used to determine the value of gravity.. FALSE
    3. The equation s = ½ (v + u)t is not an accurate equation TRUE
    4. If a body is project horizontally off of a cliff the horizontal distance is equal to the distance it would have traveled if on a straight plane FALSE, NOT SURE
    5. The equation E=mc2 invalidates the law of conservation of mass FALSE
    6. A stiletto heel shoe will cause more damage to a polished floor than a flat heel TRUE? NOT SURE, LOL.
    7. The potential energy and 1/3 height is equal to the kinetic energy at 4/6 height FALSE..EH?
    8. The mercury in glass thermometer can be used to measure bother very high and low temperatures FALSE..NOT SURE
    9. The Higher the specific heat capacity of a substance, the longer it will take to change its temperature TRUE...EH?
    10. Both evaporation and boiling of a liquid involves a change in temperature FALSE
     
  9. Jun 2, 2007 #8

    Doc Al

    User Avatar

    Staff: Mentor

    OK
    What about Galileo and his inclined planes?
    Accurate for what purpose? For uniformly accelerated motion, that equation works just fine. (Assuming u and v are the initial and final speeds over the interval t.)
    An unclear question. Whether projected off a cliff or sent along a frictionless surface, the same horizontal distance will be covered in the same time.
    Another poorly worded question. Well... if mass can be "converted" to energy, how can mass be always conserved?
    OK, due to the much greater pressure it exerts.
    Huh? Are they asking about the PE and KE of a falling object? If so, the total energy is mgh. At 1/3h, the PE is mgh/3; at 2/3h, the PE is 2/3mgh, so what's the KE?
    OK
    OK
    OK
     
  10. Jun 4, 2007 #9
    So here are the final answers after considering what you've helped me with. I still haven't figured out some [the unanswered ones].

    Yes, it's radon gas. I looked it up. Also, Carbon 14 is also known as 146C, so I got that one too. I need help with the others... I don't know if all the answers above are correct, but you can feel free to crrect me. As for my unanswered questions, below are my views on them:

    Q2. You said (a) and (c) are incorrect. So I’m going to go with:
    a. Drinking through a straw –because I think I remember learning about something around the likes of that…

    Q3. You said (a) and (b) are incorrect. I still am unsure of which is the correct answer… I am going to go with:
    b. The motion is accelerated- because velocity is a vector with both magnitude and direction and since the ball IS changing direction (it’s being spun circularly) then I’d say the velocity is changing thus there is a rate of change of velocity?

    Q7. So I found the other kinematics equation: v^2=u^2+2as
    v^2=0^2+2(10)(125)
    v^2=0+2500
    v^2=2500
    v=sqrt of 2500
    v=50m/s

    Momentum= mv = 2kg * 50 m/s = 100 kg/m/s

    Q10. I haven’t a clue about what to do with that marble question.

    TRUE OR FALSE:
    Q3. I don’t know if that equation is correct. But is there such an equation as in a standard equation not a transposed one?

    Q4. I don’t know if the distances would be the same…

    Q7. I don’t know a thing about that PE and KE thing. Can you please explain a bit more?

    I appreciate it!
     
  11. Jun 4, 2007 #10
    Q2: would a ball fall to the ground on the moon (no atmosphere)? If, by some weird chance, you think the ball needs to wear heavy boots (LOL), search for moon,falcon,feather,hammer to see a video of a feather and hammer falling simultaneously on the surface of the moon. And, guess what would happen if they opened a can of soda on the moon :) It'd probably fiz like mad! If the pressure was high enough (surface of Jupiter), it'd probably not fizz at all, provided you could get the can there before it froze) But, yes, (c) is correct. How does the liquid go up the straw? Higher pressure to lower pressure (the atmosphere provides the higher pressure.) i.e. vacuum cleaners don't "suck" - they create a lower pressure inside and the outside air pushes.


    You are correct about (3): if the direction changes, then there *is* a change in velocity (since velocity is a vector). There isn't a change in the speed (which is just the magnitude of velocity.)


    Q10: also explains why you had trouble with Q7 of T/F
    Energy is conserved. As objects fall, potential energy changes to kinetic energy, and vice versa for an object thrown (or shot, or whatever). So, when I fire a gun upward, the initial kinetic energy of the bullet as it leaves will be equal to the potential energy when it reaches its maximum altitude: this is ignoring air resistance. If we consider air resistance, then the friction of the bullet with the air is going to cause heat. The air and the bullet will heat up (slightly) - so now, the total kinetic energy = the potential energy plus the amount of energy that went into heat. (And, if you ask the question that the person looking over my shoulder asked: "I thought the bullet would be hot when it left the gun." Okay, then, the kinetic energy + heat energy of the bullet leaving = the potential energy + heat energy gained +heat energy remaining in the bullet.

    Anyway, for question 10, however much potential energy it has when it reaches its highest point will be equal (approximately) to the kinetic energy it had just as it left the ground (and equal to the kinetic energy it will have again when it's just about to hit the ground again.) Upon impact each impact, some of that kinetic energy is converted to heat, thus it won't bounce up as high. That's why it's physically impossible to drop a ball and have it rebound higher (provided there are no tricks involved, such as other ways to store energy which will later be converted to KE)

    Question 4 of the T/F could have been worded better... But, if I shoot a ball 60mph horizontally off the top of a cliff, and simultaneously, a car starts driving 60mph horizontally from the base of the cliff, then the ball will be exactly above the car the entire time. (Ignoring air resistance.)
    If a plane drops a bomb, and the plane continues flying in a straight line without accelerating, then when the bomb its the ground, it will still be exactly below the plane (ignoring air resistance again.) A bomb doesn't fall "backwards" with respect to the plane. I'll find a video for you...
    http://www.wrightwood.com/archive_film.htm look at A123-031 part way down that page; any relative backwards motion to the bombs is due to air resistance. Remember, these things are moving FAST


    And, for the last question you had trouble with:
    PE = mgh. So, at 1/10 the height, it'll have 1/10 the potential energy
    at 2/3 the height, it'll have 2/3 the original potential energy.
    at 15/27ths of the original height, it'll have 15/27ths of the original potential energy. Where does that potential energy go? (Assuming no air resistance, thus no heat), it's converted to KE. Thus, at 15/27ths the original height, 12/27'ths of the PE is lost. Where'd it go? It's now KE. The KE is now equal to 12/27ths of the original PE.
     
    Last edited: Jun 4, 2007
  12. Jun 6, 2007 #11
    So questions 7 for the T/F is TRUE...

    I still haven't figured out the question with the marble. I am guessing that it's 0.1 J using:

    0.01kg * 1m * 10ms^-2
    =0.1J?

    Is that correct?
     
  13. Jun 6, 2007 #12
    yes, the kinetic energy after striking the floor will be equal to the potential energy of the rebound ... mgh = (.010 kg)(10 m/s^2)(1) = 0.1 J
     
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