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Absolutely Basic Physics Homework HELP

  1. Sep 16, 2006 #1
    Absolutely Basic Physics Homework HELP!!!

    Hello there!
    I'm a new member and I have come across to site using google for some basic help on my physics homework!(I have just recenty started physics AP, every bit of material is new to me.) It would be extremely helpful to me if you can also help me with my high school level questions. Thank you! (this is a last resort, I have checked additional sources, I am desperate! I would much rather appreciate how to solve them than rather a direct answer.) I'm sorry if this is a long bit of work, but I'm sure it's probably very simplistic, I just don't know the proper equations to plug in.

    11.) A ball, initially a trest at t = 0 seconds, rolls down a long incline. Since the object is on the incline, its acceleration will be less than 9.8 m/s^2, althought the acceleration will still be constant. If the ball has rolled 1 meter at t = 2 seconds, how far will it have rolled at t = 4 seconds?
    (is it 2? I'm not quite sure.)

    19.) Two runners are facing each other 100 m apart. They both run toward each other. One runner runs at a rate of 4 m/s and the other runs at a rate of 6 m/s. How much distance has the 6 m/s runner traveled when he passes the other runner?

    20.) An archer shoots an arrow straight up from the surface of the Earth. When the arrow reaches its maximum height, which of the followiing would be zero?
    I. Speed
    II. Velocity

    21.) At rest, a ball is released from a height of 5 m. HOw long will it taake for the ball to reach the ground?

    23.) A car traveling at a speed of 19 m/s slows down to a speed of 2 m/s over a time period of 4 s. The distance has the car traveled in is:

    30.) A gun fires a bullet directly upward. Which of the follow best characterizes its motion at the highest point of its trajectory.
    (it states velocity downward, acceleration upward, etc etc...but is it velocity downward and acceleartion upward?)

    Ok this one I really don't get:
    34. Object A is released from rest near the surface of the moon and travels a distance d in 2.0 seconds. If object B, with a mass twice that of object A, is released from rest and allowed to fall for 1.0 seconds near the surface of the moon, the distance it will travel is:???

    38.) An object is dropped off a cliff of height h. When the object has fallen for 4 s, it has fallen a distance .55h. How long will it take to fall the rest of the way?

    39.) An object is dropped off a cliff with a height of 8m. When the rock has been falling for 4 m, its velocity is most nearly:

    45.) What is the average velocity of a car that travels 30 kilometers due west in .5 hour? (Do I state 60 km/hr west??)

    52. Which quantity is not fully specified unless its direction is given?
    a.) time
    b.) velocity
    c.) distance
    d.) mass
    e.) speed

    55.) On a displacement versus time graph, a horizontal line corresponds to motion at:
    a.)zero speed
    b.) Constannt, non zero speed
    c.) increasing speed
    d.) decreasing speed
    e.)decreasing acceleration

    60.) (this one I have no clue.) The sonar of a stationary ship sends a signal down through water. The speed of the signal is 1.5 x 10^3 meters per second. The echo from the bottom is detected 4.0 econds later. What is the depth of the water under the ship?

    A.) Distance vs time
    B.) Velocity vs Time
    C.) Acceleration vs time

    61.) The slope of a tangent to a point on the graph would tell you the instantaneous:
    A or B or C
    62.) A zero slope line would indicate constant velocity
    A or b or C
    63.) The area under the curve determines the displacement
    A or b or C
    64.) A constant positive graph means increasing velocity.
    A or b or C
    65.) A stone is dropped from the top of a cliff. After it has fallen 45 m, its speed is: (How would I solve for this???)

    I know it's a bit of a longshot writing alot of my homework down, but without my teacher or knowing any classmate, I really want to understand the material given to me.

    I'm sorry for the redundant statements, but I'm really really in need of help.
  2. jcsd
  3. Sep 16, 2006 #2


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    Staff Emeritus
    Science Advisor

    We ask that students show work and attempt solutions first before asking for assistance.

    For 11) "If the ball has rolled 1 meter at t = 2 seconds", if the initial velocity is zero, what is the relationship between distance x and time, t, with a constant acceleration? Knowing a distance and time, one can determine the magnitude of constant acceleration. Then one can solve for any x at any t.

    One will find this useful -
  4. Sep 17, 2006 #3


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    Staff: Mentor

    Do you really need help with #19? It looks to be pretty simple algebra.
  5. Oct 2, 2006 #4
    Sorry for bumping this thread but I need help on these questions:
    54.) A cannon fires a cannonball with an initial velocity of 30 m/s at an angle of 60 degrees to the horizontal. If air resisitance is negligible, the amount of time the cannonball remains in the air is
    a.)2.6 s
    b.) 3.0 s
    c.) 5.2 s
    d.) 6.0 s
    e.) 7.8 s
    ( I think I have to use 30 cosine 60 and plug it in the formula? I dunno....)

    Questions 61-62
    A child throws a baseball from an elevated position of 5 m. The baseball travels a horiziontal distance of 50 m.

    61.) How much time passes before the baseball hit the ground?
    62.) How fast did the child throw the ball horiziontally?

    64.) In a free-fall experiment, the acceleration is known to within +/- 2% and the time interval is measured to +/- 3% What would be the % uncertainty in the computed value of .5at^2?

    I am not asking for answers, but rather some help onto doing them. I'm pretty it's basic, so it shouldn't consume much time. Thank you.
  6. Oct 2, 2006 #5


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    Staff: Mentor

    You are correct, these are basick kinematic motion questions. What are the basic kinematic equations that you should use to solve them?

    What equation relates final position Y to initial position Yo, initial velocity Vo, time t and acceleration a?

    What equation relates final velocity V to initial velocity Vo, acceleration a and time t?
  7. Oct 2, 2006 #6
    http://www.glenbrook.k12.il.us/gbssci/Phys/Class/1DKin/U1L6a1.gif [Broken]
    is this it?

    So is it a matter of simply "plugging" them in?
    I dont understand the appropriate values to plug in.
    Last edited by a moderator: May 2, 2017
  8. Oct 2, 2006 #7


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    Staff: Mentor

    The first one you list is missing a di term on the right, but otherwise, yes, those are the equations you should be using. I dunno about "just plugging in", as it implies that you don't have a feel yet for why those equations are useful and how they work.

    Like on your -54- problem, you do calculate the Vi as the initial cannonball V multiplied by sin(60) or cos(30), and then use the 3rd equation that you listed above to tell you when the ball hits the ground....
  9. Oct 2, 2006 #8
    how do I find the value of Vf then?
  10. Oct 2, 2006 #9


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    Staff: Mentor

    Think about it for a sec -- if the ball if fired from ground level with an initial vertical velocity of Voy, then how fast is the ball going downward when it hits the ground? It flies up until its vertical velocity stops (due to the acceleration of gravity aiming downward), and then accelerates downward (again due to that same acceleration of gravity) until it hits the ground. What is Vyf?
  11. Oct 2, 2006 #10
    -9.8 is the acceleration of gravity onto the ball right?
    Voy = 30 m/s?

    Vyf = 30cos(60) = (30)t + 1/2(-9.8)t^2?
    Or am I completely off...
  12. Oct 2, 2006 #11


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    Staff: Mentor

    Close, but the ball is fired at an angle of 60 degrees up from the horizontal, so the verticaly velocity initially is 30 * sin(60). Keep on going, and be sure to keep checking your units as you go.
  13. Oct 9, 2006 #12
    Ok i managed to find the answer for that question, but now I'm onto something new and I have absolutely no IDEA on how to solve them!
    I also do not fully comprehend the vocabulary as well(resultants etc.), so I need someone to give me a step by step instruction on how to solve them, they probably are fairly easy but I fail to see on how to solving them. Thank you.
    1.) Find the resultant of 40.0 N at 45 degrees, 20 N at 90 degrees and 25 N at 135 degress graphically. (Don't have to draw, I just need instructions on solving this problem.)

    2.) Repeat Problem 1 by resolving each of the threee forces into its horiziontal and vertical components find the resultant of the vertical components and the resultant of the horizontal components. Use trigonometry to find the resultant of these two forces. Compare this answer to the one you obtained in problem 1.
  14. Dec 9, 2006 #13
    Does Newton's law of gravitation exist outside the earth's atmosphere?
  15. Dec 9, 2006 #14
    Yes, Pack60. That's why we remain in an orbit about the sun.
  16. Dec 9, 2006 #15
    Can someone please point me in the right direction to find the answer to this problem. I have searched and searched.

    Which of the following statements is true about the relationship between impact and impulse?

    A. impact is always greater than impulse
    B. impulse is always greater than impact
    C. impacts generate impulses
    D. impulses generate impacts
  17. Dec 9, 2006 #16
    when angular velocity is 0, is it true that angular acceleration must also be zero?
  18. Dec 9, 2006 #17
    If all other factors are held constant, what effect would "choking up" ( moving the hands away from the "handle of the bat") on a bat have on the resultant linear velocity of a hit ball?

    If the angular velocity of a batter's shoulders increases, what will happen to the linear velocity of the end of the bat?
  19. Dec 9, 2006 #18
    An increase in angular acceleration will decrease linear acceleration if the radius is held constant. (True / False)
  20. Dec 10, 2006 #19


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    Staff: Mentor

    pack60, you MUST show your work and the relevant equations. You can't just post questions and expect us to do your work for you.

    If you do it again, I'll have to start handing out warning points.
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