1 Multiple Choice Questions (40% of score)

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1 Name: Department of Physics and Mathematics Tennessee State University Physics 2110 Practice Final Exam; 100 Points Total 1 Multiple Choice Questions (40% of score) 1. Two men want to support a uniform board measuring 6 meters in length and weighing 200 N. If one man exterts 50 N of force on one end of the board, with how much force and how far from the other end must the other man hold the board to keep it horizontal and motionless? (a) 150 N, at the other end of the board (b) 150 N, 1 m from the other end of the board (c) 150 N, 2 m from the other end of the board (d) 150 N, at the center of the board (e) 150 N, 4 m from the other end of the board 2. A 13.5-kg box slides over a rough patch 1.75 m long on a horizontal floor. Just before entering the rough patch, the speed of the box was 2.25 m/s, and just after leaving it, the speed of the box was 1.20 m/s. The magnitude of the average force that friction on the rough patch exerts on the box is closest to: (a) 13.7 N (b) 5.55 N (c) 19.5 N (d) 14.0 N (e) It is impossible to know since we are not given the coefficient of kinetic friction. 3. When you blow some air above a paper strip, the paper rises. This is because (a) the air above the paper moves faster and the pressure is higher. (b) the air above the paper moves slower and the pressure is higher. (c) the air above the paper moves faster and the pressure remains constant. (d) the air above the paper moves faster and the pressure is lower. (e) the air above the paper moves slower and the pressure is lower. 4. In rotational dynamics, moment of inertia (I) plays a role analogous to one of the quantities encountered in linear motion, namely (a) mass. (b) a couple or moment of a force. (c) translational kinetic energy (d) impulse. (e) momentum. 5. Vector A has components A x = 33.2 and A y = What are its magnitude A and angle φ? (a) A = 6.67 and φ = 2.81 (b) A = 35.1 and φ = 161 (c) A = 21.8 and φ = 289 (d) A = 21.8 and φ = 341 (e) A = 44.6 and φ = 135 1

2 6. A tug boat pulls a cargo ship using a cable that makes a 20.0 angle with the horizontal. The tension in the cable is 7500 N and the cargo ship is pulled a distance of 450 m. What is the total work done on the on the cargo ship? (a) J (b) J (c) J (d) J (e) J 7. A crane uses a 10.0 m long, light, steel cable of diameter m to lift a car with weight 6000 N. The Young s Modulus of steel is Pa. By how much does the cable get stretched? (a) 10.0 mm (b) 3.82 mm (c) mm (d) mm (e) mm 8. A simple pendulum of length l has a swing period P. If the pendulum s length is quadrupled to 4l, what will be the new swing period P? (a) P/4 (b) P/2 (c) P (d) 2P (e) 4P 9. A train accelerates with constant acceleration m/s 2 from an initial velocity of 2.50 m/s moving East to a final velocity of 25.0 m/s moving East. How far does the train travel in this time? (a) 619 m (b) 625 m (c) 1240 m (d) 31.6 m (e) 55.0 m 10. A standing wave of the second overtone (counting from the n = 1 fundamental frequency being the zero overtone) is induced in a stopped pipe, 1.2 m long. The speed of sound is 340 m/s. What is the frequency of the sound produced by the pipe? (a) 213 Hz (b) 70.8 Hz (c) 354 Hz (d) 425 Hz (e) 708 Hz 2

3 2 Short Answer Questions (30% of score) 1. Explain why when an ice skater who is spinning with his arms extended pulls his arms into his body, he spins faster. 2. A dog team pulls a sled on ice with a horizontal force of 300 N, covering a distance of 15 m in 5 seconds. The sled moves on the ice without friction. What is the change in the momentum of the sled during this event? 3

4 3. Astronaut Alan Shepard famously hit a golf ball from the Moon s surface, where the acceleration of gravity is only 1.62 m/s 2. Assuming the ball launched at a speed of 25.0 m/s (his swing was slow due to the bulky space suit) and an angle of 40.0 above the horizon, how far away did the ball land? Assume a constant gravitational acceleration of 1.62 m/s 2, no air resistance (the Moon has no atmosphere), and that the surface of the Moon is flat over these distances. 4. To manouver in space, an astronaut will fire short bursts of his thrusters in the opposite direction that they want to travel, and not burn the thrusters constantly like is often potrayed in the movies. Explain how each of Netwon s 3 laws of motion play a role in such manuovers. 4

5 5. A 2.40 kg block of wood is resting on a horizontal surface. It is attached to a massless string which passes over a pulley. The other end of the string is attached to a 3.60 kg block suspended in the air. When released the 3.60 kg block begins to descend with an acceleration of 3.92 m/s 2. What is the coefficient of kinetic friction between the 2.40 kg block and the table? 6. A planet is found to be twice as massive as earth, yet half of its radius. If a 5.0 kg ball were to be dropped 10m above its surface, how long would it take to hit the ground? 5

6 3 Long Answer Questions (30% of score) 1. A solid, uniform cylinder of mass M = kg and radius R = 5.08 cm rolls at a center-of-mass speed of m/s without slipping on a horizontal surface toward a ramp that makes an angle of 25 with respect to the horizontal. You can ignore friction between the cylinder and the surface. (a) What is the moment of inertia of the rolling cylinder? (b) What is the magnitude of the angular momentum of the rolling cylinder? (c) What is the rotational kinetic energy of the rolling cylinder while it is on the horizontal portion of the track? (d) What is the linear kinetic energy of the rolling cylinder while it is on the horizontal portion of the track? (e) How far up the ramp (as measured along the ramp) does the cylinder reach before it starts to roll back down? 6

7 2. A 650 kg racecar s position on an oval track is given by r(t) = (200 m) cos(2πt/(20 sec))î + (100 m) sin(2πt/(20 sec))ĵ. (a) What is the magnitude (in m/s) and direction (in degrees, measured from the +x axis through the +y axis) of the racecar s velocity at t = 5.00 s? (b) What is its acceleration vector, in m/s 2, at t = 17.5 s? components. Give both x and y (c) What net force must be acting on the racecar at t = 17.5 to create the acceleration observed? Provide both the magnitude (in N) and direction (in degrees, as above) of the force. 7

8 3. In an experiment to find out the muzzle velocity of your BB gun, you fire a BB straight up into a wooden block of mass kg. The BB has a mass of kg. The BB embeds itself in the block, and the BB+block rises to a maximum height of 0.94 m off the table. (a) What was the kinetic energy of the BB+block just after the BB hit the block? (b) How fast was the BB+block going just after the BB hit the block? (c) How fast was the BB going just before the collision? 8

9 4. In the picture below, the mass of the fore-arm is 2.0 kg and the length L of the fore-arm is 0.56 m. (a) Find the tension T in the sling. (b) Find the x-component of the force exerted by the elbow fx. (c) Find the y-component of the force exerted by the elbow fy. (d) The sling is made of a single strip of Nylon (Youngs modulus 3.0 GPa) with a cross-sectional area of m 2. Unstretched, the sling has a length of 1.35 m. How much is the sling stretched by the tension T? 9

Tennessee State University

Tennessee State University Dept. of Physics & Mathematics PHYS 2010 CF SU 2009 Name 30% Time is 2 hours. Cheating will give you an F-grade. Other instructions will be given in the Hall. MULTIPLE CHOICE.