# oldexam2 - 2;er has” A A A A AAAA Physics 160 Exam#1...

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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 closed-book 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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