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Unformatted text preview: 2.;er .._.:,. , .. . . . has” . A A A A AAAA Physics 160, Exam #1
Monday, Feb. 25, 2008 Directions: This exam is closedbook and closed—notes. Be sure to show how
you work out the answers; with the exception of the ﬁrst problem, there will be
no points given for answers alone, even if the work involved is relatively simple. Each of the 7 problems in Part 1 is worth 10 points for a maximum of 70.
Each of the 2 problems in Part 2 is worth 15 points, for a maximum of 30. There
is an extra credit problem worth 10 points. Part 1 (70 points): Small Problems
Answer All 7 Problems (1) What are Newton’s three laws of motion? M '11:) Moon} ml rerl nuan gal reri. Chalet 900114 «(mi/J V Ail/Mam; mw Wlh' V  :74”) Em? a”) Aem— 72mins (2) Aparticle moves in the x—y plane, its location given by the coordinates
(x,y) in meters. Initially, at time t "—11.0 sec it is located at the origin, (0.0 m,
0.0 m). At t = 1.0 sec it is located at the point (1.0 m, 2.0 m). At t = 2.0 sec it
is located at the point (3.0 In, 5.0 In). What is the change in its displacement vector, éﬁ from t = 1.0 sec to t = 2.0 sec? What is the time average of the
velocity 17 over this interval? (3) A particle with mass m = 2.0 kg moving in the x direction with an initial velocity of 2.0 m/s ﬂ is subjected to a constant force of 6.0 N in What will be
the velocity of the particle after 2.0 seconds? (4) A stone is thrown vertically with an initial speed of 40.0 m/s. What is
its maximum height? (Neglect air friction.) x02: 03 + gan L"
{/x/ g .
(Uo=(t/OM/: 4X: (VON/{j rm a z: . 4.?"”/; Z gxg_gru/rq\ (5) A 5.0 kg box is pushed across the ﬂoor. When it reaches a speed of 5.0
m/s, it is released. For how long (how many seconds) will the box slide on its
own before stopping? The coefﬁcient of kinetic friction between the box and
the ﬂoor is 0.40, and the static coefﬁcient of friction is 0.50. 5'”é 6) A truck is towing a trailer on a level surface. The trailer has a mass of
5000 kg, and is attached to the truck with a chain. If the trailer accelerates at a rate of 0.15 111/52, what is the tension in the chain? (Neglect the mass of the
chain.) , 7) A 2.0 kg block of wood is gently placed on an inclined plane. Although
the plane is inclined at an angle of 30 degrees with reapect to the horizontal, the block does not move. What is the force of friction between the block and
the inclined plane? Part 2 (30 points): Large Problems
Solve Both Problems
(Partial credit will be awarded, if merited.) 1 (15 points). An "Atwood machine“ consists of two blocks attached together
by a cord and hanging from a pulley, as shown in the ﬁgure. One bleak has a.
mass of 2.0 kg, and the other block has a mass of 5.0 kg. When released, the
heavy block accelerates downwards, and the lightweight block accelerates up
wards. What is this acceleration, and what is the tension in the cord? (Neglect
the mass of the cord, and the mass of the pulley.) l
.1
4
II . 2 (15 points). A 5.0 kg block of wood is placed at the top of an inclined
ramp, inclined at an angle of 30 degrees with respect to the horizontal. The
ramp has a length of 3.0 meters. The coefﬁcient of static friction between the block and the ramp is i, and the coefﬁcient of kinetic friction is The block is given an initial velocity of 1.0 m/s in the direction down the ramp. If the
block slides all the way down the ramp, how long does it take? Alternatively, if the block doesn’t make it all the way down the ramp, then how far does it get
before it comes to a stop? Part 3 (10 points):
Optional Extra Credit 1. As part of a NASA low—gravity investigation, Alan Sheppard hit a couple
of golf balls on the surface of the moon during the 1971 Apollo 14 mission. He
estimated that one of the balls went about 400 meters. Assuming that it was
launched at the optimal angle, what was the speed of the ball when it hit the lunar surface? The strength of gravity on the moon is 1/6 its strength on the
earth, and there is no air on the moon. ...
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 Spring '08
 Walker
 Physics

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