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Unformatted text preview: Physics 171.101 Exam 2 Answers March 24, 2005
Prof. Barnett You may use anything written on the front and back of ONE 3”x5” index card.
Everything should be written in ink and no “snow paint” should be used.
Show your work. Don’t just write down an answer. Use 1. A 100 kg mass is at rest on a plank. Its coefﬁcient g = 10 m/sec2, G : 6.7 x 10—11Nm2/kg2
100 kg of static friction is as = 0.75 and its coefﬁcient of ﬁg/ kinetic friction is M = 0.60. One end of the plank is
slowly raised until it reaches an angle, 6mm, at
which the mass starts to slide down the incline. ' A) (9 pts) What is the angle 19mm? 37"
B) (8 pts) What is the magnitude of the “Normal Force” acting on the mass? 800 N. C) (8 pts) Find the magnitude of the acceleration, (i, of the mass after it starts to
slide down the incline. 1.2 m/sec2 A 1.5 kg mass is attached to a vertical spring. A student gradually lifts the mass until
she is just holding all of its weight. She suddenly releases the mass and it goes into
vertical simple harmonic motion with a TOTAL vertical range of 0.5 meters. A) (7 pts) Find the spring constant, k. 60 N/m.
B) (6 pts) Find the period of the oscillation, T. 0.99 sec.
C) (6 pts) Find the maximum speed of the mass during its oscillation. 1.58 m/ sec. D) (6 pts) Find the maximum force that the spring exerts on the mass during its
oscillation. 30 N. TURN PAGE OVER 3. A 75 kg warthog slides down a frictionless slope which is 8 meters high. At the bottom
he hits a spring which compresses by an amount X = 1.25 meters. A) (9 pts) What is the spring constant of the spring? 7680 N /m The warthog repeats the slide but this time encounters a short, rough region of 2 meters
length on the level part of the ground which is not frictionless, but which instead has a
coefﬁcient of static friction of as = 0.4 and a coefﬁcient of kinetic friction of Mk 2 0.2. B) (8 pts) How much will the spring compress when the warthog hits it? 1.22 m. C) (8 pts) The spring shoots him back across the rough dirt and up the slope. To
what maximum altitude will he now rise? 7.2 m. Frictionless ‘ I Frictionless 4. The earth’s radius is RE : 6.4 x 106 meters and its mass is ME = 6 x 1024 kg. The
sun’s radius is RS 2 7 X 108 m and its mass is Ms : 2 x 1030 kg. It is a distance of
D549 2 1.5 x 1011 meters from the sun to the earth. A) (13 pts) You want to build a rocket that will take you to another solar system.
What is the minimum velocity that would be required at the surface of the earth
to get you free from both the earth’s and sun’s gravitational attraction, i.e. let you get out of our solar system? 4.373 x 104 m/sec. B) (12 pts) Suppose you, mass(you) = 50kg, are the pilot of the space ship. How much
work did the earth’s gravitational ﬁeld do on you as you went from the earth’s surface to beyond the solar system? — 3.14 X 109 J. ...
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 Fall '08
 ProfessorHenry
 Physics

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