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STUDENT INSTRUCTION AND ANSWER
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Activity 2: Concept
Introduction The Hammer Throw
A. Watch the video
of the hammer throw (top view).
(Note: your teacher may have already downloaded this movie for you)
B. Watch the video of the hammer throw (side
view).
(Note: your teacher may have already downloaded this movie for you)
C. Is the thrower able to stay
in one location as the hammer is swung around? What object or force is
causing the thrower to move from side to side as he spins?
D. Draw four overhead sketches
(like the drawings provided in Activity 1 of the Sun and Jupiter) of the
hammer and thrower for four different instances during one complete orbit.
Include dotted circles with each sketch to illustrate the entire path
of the orbit for both the hammer and thrower (as was shown in the drawings
provided in Activity 1).
E. In each drawing mark the center of the orbit for each object.
F. Should the centers of each
object's orbit lie at the same location? If so, what is the name given
to this location? If not why not?
G. Is the location you marked closer to the thrower, the hammer, or halfway
between the two? Explain your reasoning.
H. If a more massive hammer is used, does the location of the center of
mass move closer to or farther from the hammer? Does the location move
closer to or farther from the thrower? Draw a sketch to illustrate your
answer.
I. Compare the size of the orbital paths (circles) that you drew in question
D to those that you drew in question H. Did the size of each object's orbit
increase, decrease or the stay the same?
J. If the mass of the hammer and thrower are equal how does the distance
from the center of mass to each object compare? Draw a sketch to illustrate
your answer.
K. The equation provided below is used to calculate the location of the
center of mass for a twobody system. For the thrower & hammer system
shown let the mass of the thrower m_{1} = 120 kg, the mass of the hammer
m_{2} = 40 kg. The distance from the origin to the thrower is represented
by the symbol r_{1} and the distance from the origin to the hammer is represented
by the symbol r_{2}. The values of r_{1} and r_{2} can be negative. The hammer
and thrower are 1.5 m apart.
i. Calculate the location
of the center of mass for a coordinate system with the origin chosen
to be at the midpoint between the hammer and thrower. Show your work
and mark this location in the drawing above.
ii. Calculate the location
of the center of mass for a coordinate system with the origin chosen
to be at the location of the hammer. Show your work and mark this location
in the drawing above.
iii. Calculate the location
of the center of mass for a coordinate system with the origin chosen
to be at the location of the thrower. Show your work and mark this location
in the drawing above.
L. Does the actual location
of the center of mass change with the different choices of coordinate
systems?
M. The topview path for one orbit of the thrower is shown below, the
location of the hammer has not been drawn. Using the length and size of
the rope and hammer shown below mark the location of the hammer for each
position of the thrower.
N. With each thrower location,
are there any other locations that the hammer could have been drawn at
other than the one you have shown? Why or why not?
O. At each location 14, draw a vector to represent the velocity of the
thrower.
P. If you were standing at point A, for which position(s) of the thrower
would you measure the radial velocity to be:
i. positive
ii. negative
iii. zero
Explain your reasoning.
Q. Carefully sketch a radial velocity vs. time graph for the thrower as
seen by an observer at point A.
R. How would you change the above graph if it were made by an observer
at point B? Explain your reasoning.
