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Unformatted text preview: Physics 221 — Fall, 1990
Laboratory Final This laboratory final consists of 8 questions, each worth 2 points toward your
total score for the course. 63. Measurements of physical quantities are often quickly repeated several
times, one after the other. Which of the following is NOT a good reason
for this practice? A. To look for some degree of reproducibility in the measurements, a characteristic that is expected in many physical systems.
To determine the systematic error that may be present.
To estimate the random uncertainty in each measurement. D. To determine the average of many measurements, because such
averages typically have smaller random uncertainties that the
corresponding individual measurements. ' E. To determine if the measurement fluctuations are consistent in size
with the type of system being observed and instruments being used. 64. If the result of a measurement is determined to be 0.0002605 i 0.01,
which of the following expresses the measured value in a form consistent
with standard practice in the use of significant figures? A. 0.00026 B. 0.01 C. 2.6 X 10'“ D. 0.0002 65. A record of the speedometer readings
are made for two separate trial runs
on straight roads of the latest
reject from the local Rent—a-Wreck.
The readings are given in miles per
hour. Which of the following statements accurately and most completely
describes the motion of the vehicle? The vehicle is moving. The vehicle_ s moving with constant acceleration. The vehicle is moving with a constant acceleration ofvS mph/s/s.
The vehicle is accelerating at a rate which is not constant. The position of the vehicle is a quadratic function of time. P. 1119061? 20-”0 __ 4 moh
‘” s 5+05“s.>= 5’ gar—20 _, 2L (5‘ JD 10 5) = r '3 “‘5‘ a; (,5— 4—0 1053‘:— 5‘0"”; z wags/2. 66. In laboratory, the time required to reach the floor for a ball fired
horizontally or simply dropped vertically from the top of a lab table was
found to be approximately 0.42 5. Approximately how long (in s) does it
take for a second ball with the same volume but twice the mass density to
reach the floor when dropped from the same elevation? @ a. 0.59 -r c. 0.84 n. 0.30 E. 0.21 67. Consider the collision of two identical hockey pucks on a smooth ice
rink. Assume that by analyzing the videotape of the collision, various
but not all components of the momenta of the two pucks before and after
collision have been determined and are recorded in the table below. Assume that there is negligible friction with the ice, but that the pucks
are made of soft iron (like those used in lab), and are left dented by
the collisions. What principle(s), if any, can one use to determine the value of the
entry marked "x" from the data shown below. Before collision After collision The entry marked "x" cannot be determined from the data shown.
Conservation of energy Conservation of energy and linear momentum
Conservation of angular momentum A
<::::> Conservation of linear momentum 68. The motion of a flywheel is monitored
by an encoder which produces 200
pulses for each revolution. The
wheel is allowed to gradually slow
down and stop; the number of pulses
produced in each succeeding one— _ second interval is plotted at the
right. wig“ mv z 0.25'ACN/S
S .._..— 7_ . 9-0-0)?
Estimate (if possible) the wheel’s angular speed (in revolutions/s) at
the time t = 6 s. A. 0.05; ' B. 5 c. 63 ® 69. Consider two metal cans, each perched
atop an electroscope. Assume the right one is charged, the left one
not. By which procedure described
below can one move essentially the entire net charge from the right can to the left can? w‘dU/J‘ﬁj A Move the right can 0 tha it touches the left can. B. Move the left can 0 that it touches the right can. ‘
<::Z:> Repeatedly touch ball (on an insulated handle) to the outside of D E the right can and the inside of the left can. Repeatedly touch a ball (on an insulated handle) to the outside of
the left can and ﬁﬁe inside of the right can. None of the above since the best one can do by simple mechanical
means is to equalize the charge (it’s like water seeking the same
level everywhere). 70. Consider two identical conducting
spheres hung from insulating threads
and located in a region of large
electric field, such as near a +
charged rod as shown. +
Assume the two spheres are initially '
uncharged. Then, one of the two is
displaced slightly so that the tho . ‘ \
L + touch briefly. After this, assume that one of the
two spheres has a net charge of
+8 nC. What can one say about the charge carried finally by the sphere on the
left? A. It is the one with a charge of +8 nC. ‘5;
It must carry a charge of —8 nC. C. It must be uncharged.
D.’ It must carry a charge of +4 nC (the average of O and +8 nC). \7P\
One cannot say anything without more information. ,3 E.
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- Spring '08
- Momentum, net charge, identical hockey pucks, smaller random uncertainties, entire net charge