<p>October 12th-October 13th, 2009 PHY 2048 Discussion Fall ’09 Conceptual Review: Chapter 8.5-9.12 A . Work-Energy Theorem 1. Write down the work-energy theorem in two ways.</p><p>2. Only conservative forces are exerted on an object. What quantity is conserved? </p><p>3. A figure on the right shows a mass m attached to a string of negligible mass. What initial velocity do you need to give at the lowest point for the mass to take a circular path? </p><p>4. A block with an initial velocity v slides along a track that descends through a vertical distance h. The track is frictionless except for the lower section; there the block slides to a stop in a distance D due to friction. What is the change in thermal energy of the system? Does it depend on D? </p><p>B. Center of Mass 1. Three uniform thin rods form an inverted U as shown, where L = 20 cm, M = 40g and m = 30 g. Find the center of mass.</p><p>C. Impulse-Momentum Theorem 1. A 2-kg ball drops vertically onto a floor, hitting with a speed of 20 m/s. It rebounds with an initial speed of 10 m/s. If the ball is in contact w/ the floor for 0.05s, what is the average force exerted on the ball by the floor? </p><p>D. Conservation of Momentum 1. Under what condition is the momentum of a system conserved?</p><p>2. A 100-kg man on a frictionless surface fires a gun and a 0.01-kg bullet is shot at a speed of 500 m/s. What speed does the man acquire? </p><p>3. In the figure on the right, block 1 of mass 3-kg hits block 2 of mass 2 kg with a speed of 5m/s. The block 2 is initially at rest. Then they stick together and slide on a frictionless surface. The force constant of the spring is 200 N/m. Find the maximum compression. October 12th-October 13th, 2009 PHY 2048 Discussion Fall ‘09 Practice Exam Problems (Chapter 8.5-9.12) 1. The potential energy of a 0.20-kg particle moving along the x axis is given by U(x) = (8.0J/m2)x2+(2.0J/m4)x4. When the particle is at x = 1.0 m it is traveling in the positive x direction with a speed of 5.0 m/s. It next stops momentarily to turn around at x = : (Potential Energy Function) a. 0 b. -1.1 m c. 1.1 m d. -2.3 m e. 2.3 m</p><p>2. A small ball of mass ma starts from rest at the position shown and slide along the frictionless loop-the-loop track of radius R. What is the smallest value of y such that the object will slide without losing contact with the track? (Conservation of Energy) a. R/4 b. R/2 c. R d. 2R e. zero</p><p>3. A 0.75-kg block slides on a rough horizontal table top. Just before it hits a horizontal ideal spring its speed is 3.5 m/s. It compresses the spring 5.7 cm before coming to rest. If the spring constant is 1200 N/m, the thermal energy of the block and the table top0 must have: (Thermal Energy) a. not changed b. decreased by 1.9 J c. decreased by 2.6 J c. increased by 1.9 J e. increased by 2.6 J</p><p>4. The x and y coordinates of the center of mass of the three-particle system shown in the figure are: (Center of Mass) a. 0, 0 b. 1.3 m, 1.7 m c. 1.4 m, 1.9 m d. 1.9 m, 2.5 m e. 1.4 m, 2.5 m </p><p>5. A 0.2-kg rubber ball is dropped from the window of a building. It strikes the sidewalk below at 30 m/s and rebounds up at 20 m/s. The impulse on the ball during the collision is: (Impulse-Momentum Theorem) a. 10 Ns upward b. 10 Ns downward 2.0 Ns upward d. 2.0 Ns downward e. 9.8 Ns upward</p><p>6. A 3-g bullet is fired horizontally into a 10-kg block of wood suspended by a rope from the ceiling. The block swings in an arc, rising 3 mm above its lowest position. The velocity of the bullet was: (Collision) a. unknown since the heat generated in the collision was not given b. 8.0×10 2 m/s c. 24.0 m/s d. 8.00 m/s e. 2.4×104 m/s</p><p>7. A rocket exhausts fuel with a velocity of 1500 m/s, relative to the rocket. It starts from rest in outer space with fuel comprising 80 per cent of the total mass. When all the fuel has been exhausted its speed is: (Rocket Motion) a. 3600 m/s b. 2400 m/s c. 1200 m/s d. 880 m/s e. 400 m/s Answers: 1-c 2-b 3-e 4-c 5-a 6-b 7-b</p>