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Unformatted text preview: Physics 171il01 Exam 3 Answers April 17', 2008
Prof“ Barnett You may use anything written on the front and back of ONE 3”}: 5” index card“
Everything shouid be written in ink and no “snow paint” should be used Use Sin(37°)=0.6, Cos(37°)m08, igg = 10 m/sz, 1553;; ﬁlms“ R = (2/5)MR2. Write the foilowiiig two sentences Onto the cover of your blue book and sign it.
I agree to complete this exam without ieceiving unauthorized assistance from any pezson or device.
I will not reveal the contents of this exam to any unauthorized persons 1‘. A ball, 8;, of unknown mass trawling in the “x” direbtion strikes
two other balls each with a mass of 02 kg. The original hall
comes to rest. The coliision is compietely elastic. The other two '5:
balls move off at angles of" 53" and 37" as shown in the picture" The speed of one ball, .32, is 10 111/ sec after the collision as shown
in the picture. Ignore friction and rolling in this problem" A (9 pts) What is the speed of the second ﬁnal: ball, B3? 75 m/sec )
B) (8 pts) What was the momentum and kinetic energy of the original bail, B}?
P m 25 kg Iii/Sec KE = 15.625 .3 C) (8 pts) What was the mass and speed of the original ball, Bl?
M m 02 kg, V = 12.5 m/secu 2.. A uniform solid sphere with radiusilil Meters and mass 5 kg
is at rest at the top of an inclined plane" The piane makes an
angle of 37° to the horizontal and is 5 meters iong. rThe sphere
rolls without slipping down the plane until it gets to the bottom“ Irggtmcmwfphere m gzla m/Secfzh A) (10 pts) What is the speed of the sphere, ie. its center of
mass, when it gets to the bottom of the piano?
V m 6.55 111/330. 13) ( 8 pts) What is the acceleration of the sphere, ie: its center
of mass, as it rolls down the plane? a m 4.286 iii/sec2 C) (7 pts) What is the magnitude of the frictional force acting
on the Sphere as it rolls down the plane? Flewmm = 8 57’ N TURN PAGE OVER 3,, A uniform, cubical block is suspended from a scaies above
a vat of fluid, The block is slowly lowered into the fluid,
The reading of the scaies, in kilograms, is shown in the
ﬁgure versus the distance the block is lowered. Scale reading (kg) A) (7 pts) What is the iength of a side of the block?
15 cm B) (8 pts) What is the density of the block?
2.67 x 103 kg/m3 C) (10 pts) What is the density of the ﬂuid?
L04 X 103 icg/rn3 4" A square wire, with an edge length of 1 mm, is 2.5 meters long.
It has a. density of 4 grams/cm? A 100 kg mass hangs on the
wire For uniformity, let’s all set X = 0 meters to be the piece
where the wire connects to the ceiiing and X z 2.5 meters to
be the location of the 100 kg mass. , ‘100 kg‘ A) (9 pts) If a wave pulse travels on this wire, what is the speed, is phase veiocity, of the
wave pulse? 500 m/sec B) (4 pts) If a standing wave is eStablished on the wire representing the first over tone (second
harmonic), what is the wavelength of the wave? 2.5 meters C) (4 pts) For this second harmonic standing wave, what is the frequency of the vibration?
200 Hertz D) (8 pts) Write the formula for this second harmonic standing wave if the maximum dis
placement of the wire is 1 ram and the displacement is“zero" , i..e, Y‘(X, t m G) = O, for
ail parts (ail values of X) of the wire at t20, mm) m 1.0_sin(3§—§<)sin(§~,%g) mm, . 7
Here “X” is in meters and “t” is in seconds; The “Y” displacement is in millimeters, ...
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 Spring '08
 ProfessorHenry
 Physics, pts, Kilogram, blue book, Barnett, Harmonic standing wave, radiusilil Meters

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