31 January 2013

Physics Homework Ch3

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PLEASE FORGIVE my voice quality in these (Chapter 3) videos. I made them while suffering from a severely sore throat.

1. Vector A has a magnitude of 31 units and points in the positive Y-direction. When vector B is added to A, the resultant vector A+B points in the negative y-direction with a magnitude of 17 units. Find the magnitude and direction of vector B?
Direction (+x, -x, +y, or -y)?

2. Vector A has a magnitude of 8.00 units and makes an angle of 45 degrees counter-clockwise from the positive x-axis. Vector B also has a magnitude of 8 units and is directed along the negative x-axis.
a). Using the graphical methods, find the vector sum, A+B. (Do this on paper. Your instructor may ask you to turn in this work).
b). Using the graphical methods, find the vector difference, A-B. (Do this on paper. Your instructor may ask you to turn in this work

3. A plane flies from base camp to lake A, a distance of 280 km at a direction of 20.0 degrees north of east. After dropping off supplies, the plane flies to lake B, which is 190 km and 30.0 degrees west of north from lake A. Graphically determine the distance and direction from lake B to the base camp. (Do this on paper. your instructor may ask you to turn in this work).

4. A force F1 of magnitude 6.60 units acts on an object at the origin in a direction θ = 26.0 degrees above the positive x-axis. (see the figure below). A second force F2 of magnitude 5.00 units acts on the object in the direction of the positive y-axis. Find graphically the magnitude and direction of the resultant force F1 + F2
Magnitude ________ Units
Direction __________ degrees counterclockwise from the +x axis

5. A person walks 30.0 degrees north of East for 3.30 km. How far due north and how far due east would she have to walk to arrive at the same location?
North ________ km
East __________km

6.The magnitude of vector A is 39.5 units and points in the direction 330 degrees counterclockwise from the positive x axis. Calculate the x and y-components of this vector
Ax = __________ Units
Ay = __________Units

7. A girl delivering newspapers covers her route by traveling 8.00 blocks west, 4.00 blocks north, and then 4.00 blocks east.
a). What is her resultant displacement?
_____ blocks
b). What is the total distance she travels?
_____ blocks

8. A vector has an x-component of -27.0 units and a y-component of 30.0 units. Find the magnitude and direction of the vector.
magnitude ______ units
direction ______ degrees (counterclockwise from the +x-axis)

9. The eye of a hurricane passes over Grand Bahama Island in a direction 60.0 degrees north of west with a speed of 44.0 km/h. Three hours later, the course of the hurricane suddenly shifts due north, and its speed slows to 22.0 km/h. How far from Grand Bahama is the hurricane 4.40 h after it passes over the island?

Purchase the Calculator for Chapter 3 Problem 9 ($1.35)

10. A map suggests that Atlanta is 730 miles in a direction 5.00 degrees north of east from Dallas. The same map shows that Chicago is 560 miles in a direction 21.0 degrees west of north from Atlanta. The figure below shows the location of these three cities. Modeling the Earth as flat, use this information to find the displacement from Dallas to Chicago.
Magnitude _______mi
Direction _______ degrees north of east of Dallas

11. A commuter airplane starts from an airport and takes the route shown in the figure below. The plane first flies to city A, located 175 km away in the direction 30.0 degrees north of east. Next, it flies for 150 km 20.0 degrees west of north, to city B. Finally, the plane flies 190 km due west, to city C. Find the location of city C relative to the location of the starting point.
Distance ________ km
angle _________ degrees west of north

12. The helicopter view in the figure below shows two people pulling on a stubborn mule. (Take F1 = 146 N and F2 = 79.0 N).

a) Find the single force that is equivalent to the two forces shown above.
Magnitude __________ N
direction _________ degrees counter clockwise from the x-axis

b) Find the force that a third person would have to exert on the mule to make the net force equal to zero.
Magnitude ________ N
direction _________ degrees (counterclockwise from the x-axis)

13.One of the fastest recorded pitches in major-league baseball, thrown by Tim Lincecum in 2009, was clocked at 101.0 mi/h (see the figure). If a pitch were thrown horizontally with this velocity, how far would the ball fall vertically by the time it reached home plate, 60.5 ft away?
______ ft

14. The best leaper in the animal kingdom is the puma, which can jump to a height of 3.7 m when leaving the ground at an angle of 45 degrees. With what speed must the animal leave the ground to reach that height?

Another way to solve this problem:

15. A place-kicker must kick a football from a point of 36.0 m (about 40 yards) from the goal. Half the crowd hopes the ball will clear the crossbar, which is 3.05 m high. When kicked, the ball leaves the ground with a speed of 22.8 m/s at an angle of 50.0 degrees to the horizontal.
a). By how much does the ball clear or fall short (vertically) of clearing the crossbar? (Enter a negative answer if it falls short).
b). Does the ball approach the crossbar (and cross above or beneath it) while still rising or while falling?

16. A brick is thrown upward from the top of a building at an angle of 20 degrees to the horizontal and with an initial speed of 12 m/s. If the brick is in flight for 3.0 s, how tall is the building?
_______ m

17. An artillery shell is fired with an initial velocity of 300 m/s at 55 degrees above the horizontal. To clear an avalanche, it explodes on a mountainside 43.0 s after firing. What are the x- and y-coordinates of the shell where it explodes, relative to its firing point?
x =  ______ m
y = _______ m

18. A fireman d = 56.0 m away from a burning building directs a stream of water from a ground-level fire hose at an angle of θi = 24.0 degrees above the horizontal as shown in the figure. If the speed of the streram as it leaves the hose is vi = 40.0 m/s, at what height will the stream of water strike the building?
________ m


  1. Mike,

    On questions 4 and 8, I follow along with the entire problem until you get to doing the tan part. You do tan(-1)*whatever the number is and it equals the degrees of the angle.

    I am not getting the degrees when I do this on my work. I must be doing something wrong.

  2. 1st, let's make sure you're using the calculator correctly:
    If you're using a TI 84, you'll want to make sure you are in "Degrees" mode instead of "Radians" mode. To check:
    a. press "mode" (it's right next to the 2nd button)
    b. the third or fourth row down should have a highlighted selection where you can toggle between degrees and radians
    c. Select "degree" and press enter
    d. The hit second and quit.
    This video shows how to change between

    Next, when you have it set in degrees, you should be able to:
    a. Press 2nd Tan
    -- You'll now see "tan^-1("
    on your screen
    b. Type in the "Opposite/Adjacent"
    c. Close parenthesis
    d. Press enter
    -- You'll now see the angle as your answer.

    LMK if you're using a different calculator... Or just tell me the numbers for your Opposite and the number for your adjacent and I'll plug it in my calculator (won't help you on a test, but it will give you answer).

  3. I was able to Google my answer and that was my problem. It was not set to degrees. Thank you!

  4. Hi, on the 4th question I do not understand the part on finding x2 and y2.

    Please help.

    1. When dealing with vectors, you can add the components of the vecter to arrive at what is called the "resultant vector".

      I'll try to explain with an example from displacement:
      Suppose you displaced something directly along the "x" axis to the right by 5 units, then again, to the right by 2 units, then to the left by 3 units. since this is all one dimension, you can just add up the "x" values as "x1 = 5; x2 = 2, and x3 = -3
      5+2-3 = 4
      However, if you were working in two dimensions, you would also have to add up the "y" displacement values.

      So, for two dimensions, suppose you moved at 45 degrees above the "x" axis a total distance of 4.25 units, then you traveled 45 degrees above the negative "x" axis a total of 2.82 units,
      in the first leg (x1,y1), the pythagorean therom would indicate that you moved on the x axis by 3 units, then you moved up the y axis by 3 units, giving a total displacement of 4.25 units away from the starting point.
      Then in the second leg of the trip, (x2,y2) you moved left on the "x" axis by 2 units, then up the y axis by 2 units.

      To find the final position (X , Y) you add up your X components (3-2=1) and your Y components (3+2=5) and your final position is at (1,5)

      To summarize, the "Resultant" X-value can be found by adding up each of the individual X-vectors (x1,x2,x3...) and then the same holds true for the Y-value.

      If that doesn't clear things up, I may try to put it in a video to show exactly what I'm saying, so let me know.

  5. Learn first before teaching noob you have mental problems and learn to teach fisics

    1. Please explain your copmlaint. You either have a valid complaint or your just a spam bot. Those are the two possibilities.
      I have accurately explained every single question on this blog. I completed Physics with an "A". I'm now taking physics II and I still stand by these videos as accurate and helpful.
      I have admitted (on several occasions) that there have been better ways of solving a problem, and in those cases, I have either re-made the video, or made a second video to explain how to do the problem easier.

      So, if you have a valid complaint, please let me know what it is and I'll try to correct it for you.

      However, judging from your spelling, your just a spam bot. "Physics" is not spelled with an "F"


  7. The eye of a hurricane passes over Grand Bahama Island in a direction 60.0° north of west with a speed of 40.5 km/h. Three hours later, the course of the hurricane suddenly shifts due north, and its speed slows to 26.5 km/h. How far from Grand Bahama is the hurricane 4.35 h after it passes over the island?

    Can you solve this for me please? I tried to follow your example above, but got stumped?

    1. Courtney,

      I posted a link directly under the question. I created a calculator that you are free to purchase. It will calculate the answer to the problem regardless of what your variables are.

      I've been creating these calculators for all of my Physics II problems. Some of them I've left for free (to try out) and others require purchase.

      If you want to see how it will work before you pay, go to the Chapter 16 homework problems and download one of the free ones

  8. This comment has been removed by a blog administrator.

  9. Hey! I just want to let you know that I am really thankful for you showing these problems, i have a lot of struggle with physics, i am interested in medicine too, i hope to get in, although i am just in highschool, i find this really hard, but i thank you for simplificating my life, i can do my hw now, and understand it, although i know i will still do bad on tests ;/ do you have any suggestions?

    1. Being still in highschool, I would say, you're probably safe. Medical school didn't look at any of my highschool records (a very good thing), however, in order to get into medical school, you do need to be able to think through physics, and take a test called the "MCAT" (assuming you're applying in the United States).

      My suggestion is to do your homework, then take a night off, and then work through the same homework problems again. Then do it again. Do it until you get to the point where you can explain it better than I did. Because trust me, as I look back through these old videos, I realize how embarrasing they are. They can bee done better. I got better by tutoring others, and by making these videos. It required me to work through the problems more than just once.

      In short, I'll tell you what a wise man once told me: "Repetition begets retention. And retention begets second nature."

  10. How did you find the acceleration for 16?

  11. Thank you so much! your video help a lot. I have ap physic and your video is a great help.

  12. Help! A hiker walks 2.50 km north and then 3.90 km west, all in one hour and ten minutes.? (a) Calculate his average speed in km/h. (b) Calculate the magnitude of his average velocity.