# hour 3 - University of Minnesota Name: School of Physics...

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Unformatted text preview: University of Minnesota Name: School of Physics and Astronomy Student ID No: Physics 1301, Section 200, Fall 2008 TA Name: Hour Exam 3: Problem 1 (Friday, October 31, 2008) [Please do the problem on the front and back of this sheet of paper.] A horizontal force of 25 N is applied to a 4 kg block, which is initially at rest on a horizontal table. The coefficient of static friction between the block and the table is 0.50. The coefficient of kinetic friction between the block and the table is 0.35. The horizontal force moves the block through a distance of 3.00 m along the top of the table. (a) How much work does the force do on the block table system in moving the block 3.00 m? (5 points) (b) How much energy is dissipated through friction while moving the block 3.00 m? (5 points) (c) What is the kinetic energy of the block after it has been pushed 3.00 m by this force? (5 points) (d) What is the momentum of the block after it has been pushed 3.00 m by this force? (5 points) (e) How long was the 25 N force applied to move the block 3.00 m? (5 points) University of Minnesota Name: School of Physics and Astronomy Student ID No: Physics 1301, Section 200, Fall 2008 TA Name: Hour Exam 3: Problem 2 (Friday, October 31, 2008) [This problem is similar to the "Optional Homework Problem", Chapter 7, Problem 64. Please do the problem on the front and back of this sheet of paper.] A simple pendulum has a length of 1.50 m and a mass of 0.500 kg. It is released from rest at an angle of 10 below the horizontal. When the mass is at its lowest point, the string wraps around a nail located 1.20 m below the pendulum support point. (a) What is the velocity of the pendulum at its lowest point? (5 points) (b) After the pendulum string wraps around the nail, the pendulum bob swings up to its new high point. What is the velocity of the pendulum bob at this new highpoint? (5 points) (c) What are the direction and magnitude of the tension in the pendulum string at the new high point? (10 points) (d) After passing through the high point, the pendulum bob continues its swing. What is the speed of the pendulum bob when it is the same height as the nail? [5 points] University of Minnesota School of Physics and Astronomy Physics 1301, Section 200, Fall 2008 Hour Exam 2: Multiple Choice (Friday, October 10, 2008) [Please mark the answers to the problems below on the bubble sheet. Each question is 5 points.] 1. A water molecule consists of an oxygen atom (O) with a mass of 16 amu and two hydrogen atoms (H) with masses of 1 amu each. The distance OH is 9.6 nm. The angle OH O is 104.5. Where is the center of mass of the water molecule? (a) At the center of the oxygen atom. (b) Midway between the centers of the two hydrogen atoms (c) Along a line that goes through the center of oxygen atom and midway between the two hydrogen atoms; 0.96 nm from the center of the oxygen atom (d) Along the line described in part (c), 0.66 nm from the center of the oxygen atom (e) Along the line described in part (c), 0.58 nm from the center of the oxygen atom 2. A projectile is fired into the air over level ground with an initial velocity of 24.5 m/s at an angle of 36.9 above the horizontal. The expected range of this projectile is 58.8 m. However, at its highest point, the projectile breaks into two equal pieces. One piece falls directly to the ground with no further horizontal motion. How far from the firing point does the other piece land? (a) 29.4 m (b) 58.8 m (c) 88.2 m (d) 118 m (e) 236 m 3. A runaway 14,000 kg railroad car is rolling at 4.00 m/s towards a switchyard. A sudden rainstorm fills the opentop car with an 2,000 kg of rain water. After the rainstorm, how long does it take the car to reach the switchyard, which is 500 m distant from its position at the time of the rain. [Assume no friction. Also, assume that the rain fell straight down and filled the car in a negligible time interval.] (a) 103 s (b) 127 s (c) 143 s (d) 164 s (e) 189 s 4. A certain onedimensional system has a potential energy function that is shown in the graph below. Which of the following statements are true. I. The system has at least three equilibrium points. II. The force is the strongest at a point where x is positive. III. There are two stable equilibrium points. (a) Statement I only. (b) Statement II only. (c) Statement III only. (d) Statements I and II only. (e) Statements II and III only. 5. Which of the following statements are true? I. The change in momentum is proportional to the product of force times distance. II. A force applied at a point other than the center of mass does not result in an impulse. III. Momentum and kinetic energy are both conserved in elastic collisions. (a) Statement I only. (b) Statement II only. (c) Statement III only. (d) Statements I and II only. (e) Statements II and III only. U(x) x ...
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## This note was uploaded on 10/07/2009 for the course PHYS 1301W taught by Professor Marshak during the Fall '08 term at Minnesota.

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