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P113 University of Rochester NAME _________________________________________ S. Manly Fall 2003Exam 1 (October 9, 2003)Please read the problems carefully and answer them in the space provided. Write onthe back of the page, if necessary. Show all your work. Partial credit will be givenunless specified otherwise.Problem 1 (10 pts, no partial credit):An 80 kg man on ice skates pushes a 40 kg boy, also on skates, with a force of 100 N. The magnitude of the force exerted by the boy on the man isa) 200 Nb) 100 Nc) 784 Nd) 392 Ne) zero unless the boy pushes back.Problem 2 (10 pts, no partial credit):My friend Chaz drives around a city looking for a specific restaurant where he is supposed to meet a friend. Being new to the town, he gets lost. In strict accordance with the rules and bylaws of the International Organization of Males, Chaz refuses to stop and ask someone for directions. Instead, he drives around randomly looking for the restaurant.Suppose Chaz drives 4 blocks north, then 5 blocks east, then 4 blocks south, and finally, 3 blocks west, what is the magnitude of Chaz’s displacement from his starting point?a) 5 blocksb) 8.12 blocksc) 6.4 blocksd) 2 blockse) 16 blocksP113 University of Rochester NAME _________________________________________ S. Manly Fall 2003Problem 3 (10 pts):Two objects are sliding at the same speed across a wooden surface. The coefficient of kinetic friction between the first object and the surface is twice that between the second object and the surface. The distance traveled by the first object before it stops is S. The distance traveled by the second object isa) Impossible to determine without knowing the masses involved.b) 2Sc) S/2d) Se) 4SShow your work/reasoningProblem 4 (10 pts): If you jump from the top of a table to the floor, why is it best to flex your knees when you land (as opposed to landing with locked knees)? (Briefly discuss referring to physics concepts we have studied recently. Feel free to make and refer to sketches as needed.)1) /102) /103) /104) /105) /106) /107) /128) /139) /15____________tot /100P113 University of Rochester NAME _________________________________________ S. Manly Fall 2003Problem 5 (10 pts):A particle travels in one dimension. The graph below shows the velocity of a particle as a function of time. In the 12 seconds shown, the particle travels a distance ofa) 0 mb) 1200 mc) 640 md) 440 me) 200 mShow your work/reasoningProblem 6 (10 pts):Consider the vector jiAˆ12ˆ5 .a) What is A?b) What is the angle of A with the positive x axis?Now, let jiBˆ7ˆ2 .c) What is BAC ?00246 8 10 12Time, in seconds20406080100120Velocity, in m/sP113 University of Rochester NAME _________________________________________ S. Manly Fall 2003 Problem 7 (12 pts):Jed Cool rigs up a nifty system to raise a case of soda pop from the ground to the second floor balcony of his fraternity house,as shown in the sketch below. Okay, to make this more realistic, maybe it is a case of lemonade. In Jed’s scheme, he attaches a (massless) rope to the case of drinks and passes it over a massless and frictionless pulley. Then he pulls on the rope and raises the case of drinks up to the balcony level where a friend grabs the soda. The case of soda has a mass of 10 kg. Jed has a mass of 80 kg. What is the maximum acceleration Jed can give to the case of soda by pulling downward on the rope, assuming Jed’s feet never leave the ground? Show your work.P113 University of Rochester NAME _________________________________________ S. Manly Fall 2003Problem 8 (13 pts): During war games at a military base, a jet aircraft has a speed of 350 km/h and is diving at an angle of 30 degrees below the horizontal when the pilot releases a practice bomb. The horizontal distance from the point of the bomb release to the point where it hits the ground is 900 meters. a) How long is the bomb in the air (after release)? b) How high was the aircraft when the bomb was released? (Assume this is *not* a “smart” bomb. The motion is ballistic. Ignore air friction. Show yourwork and reasoning in order to receive credit.)P113 University of Rochester NAME _________________________________________ S. Manly Fall 2003Do not work on this problem until you have done/checked all the other problemsProblem 9 (15 pts):Two blocks sit on a spinning disk as shown below. They start out at rest with respect to the surface of the disk, i.e., they move in a circle as the disk spins. The rate of rotation of the disk slowly increases with time. The mass of the top block is m=1.5 kg. The mass of the bottom block is 2.5 kg. The coefficient of static friction between the bottom of the top block and the top of the bottom block is µs1=0.2. The coefficient of static friction between the bottom of the bottom block and the surface of the spinning disk is µs2=0.1. The blocks are centered at a radius of R=0.5 m from the center of the spinning disk. For simplicity, ignore the fact that the blocks have a finite extent along the radial direction. That is to say, you only need to worry about the radius R and not the transverse size of the blocks. Eventually,as the disk rotation rate increases, either the top block will slip on the top of the bottom block, or the two block combination will slip with respect to the disk surface. Where does the slippage occur? What is the minimum tangential velocity of the blocks when the slippage occurs? You must show your calculations/reasoning in order to receive credit.RSide viewTop viewP113 University of Rochester NAME _________________________________________ S. Manly Fall 2003Solution to problem 9 continued:P113 University of Rochester NAME _________________________________________ S. Manly Fall 2003 rmvFNμFNμFamFadtvvvdtxx)x2a(xvvt2vvxxat21tvxxatvvadjopptanθhypadjcosθhypoppsinθ2lcentripetasfrictionkfrictionttottoo2o2oo2ooooo 1)(11nxdxxnxdxxdnnnn aac24bb- equation quadraticrcircle of arear2circle of


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ROCHESTER PHY 113 - PHY 113 Exam 1

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