# PY205N Spring The vectors a, b, and c. are related by c = a b. The diagram below that best illustrates this relationship is (a) I

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1 PY205N Spring 2013 Final exam, practice version MODIFIED This practice exam is to help students prepare for the final exam to be given at the end of the semester. Please note that while problems on this practice exam have come from other sources and thus may be familiar, all final exams questions used in this course are newly constructed each semester. Thus students should not expect to memorize particular problems anticipating seeing them on the final. All problems on final exams (practice or otherwise) appeal to the same physical principles. The skills students develop in solving problems on a practice exam are identical to the skills needed to solve similar (but not identical) problems on the actual final exam. Data: Acceleration of gravity g = 9.8 m/s 2 ; gravitational constant G = N m 2 /kg 2 ; moments of inertia of thin rod about center, sphere, disc, and hoop: (1/12)mr 2, (2/5)mr 2, (1/2)mr 2, and mr 2, respectively; density of water ρ W = 1000 kg/m 3 ; 1 atm = N/m 2 ; (temperature in Kelvin) = (temperature in C) + 273; universal gas constant R = 8.31 J/(K mol); Boltzmann constant k B = J/K. 1. The sun is approximately a sphere of radius m. The surface area of the sun in km 2 is (a) km 2 (b) km 2 (c) km 2 (d) km 2 (e) km 2 2. Two bodies are falling with negligible air resistance, side by side, above a horizontal plane, when one of the bodies is subjected to a horizontal acceleration during its descent that continues until it lands. The correct statement of the following is: (a) The body strikes the plane at the same time as the other body (b) The body strikes the plane earlier than the other body (c) The vertical component of the velocity of the body is altered (d) The vertical acceleration component of the body is altered (e) The body follows a straight-line path along the resultant acceleration vector 3. The vectors a, b, and c are related by c = a b. The diagram below that best illustrates this relationship is (a) I (b) II (c) III (d) IV (e) none of these

2 4. Rain is falling vertically downward with a velocity of 2.0 m/s relative to the ground. A car drives horizontally through the rain. The driver of the car sees raindrops falling at an angle of 72 with respect to the vertical (slanting in at 18 from the horizontal). The speed of the car is (a) 1.9 m/s (b) 5.0 m/s (c) 0.62 m/s (d) 2.0 m/s (e) 6.2 m/s 5. The mass of a bedroom bureau that is loaded with clothing is m = 40 kg. If the coefficients of static and kinetic friction between the bureau and the floor are µ s = 0.46 and µ k = 0.23, respectively, the minimum horizontal force that is required to start the bureau sliding is (a) 4.5 N (b) 45 N (c) 90 N (d) 120 N (e) 180 N 6. A 1000 kg elevator is rising with a speed that is increasing at 3 m/s 2. The tension in the cable lifting the elevator is (a) 6800 N (b) 1000 N (c) 3000 N (d) 9800 N (e) N 7. A passenger weighing 800 N pushes against a car door with a force of 200 N when the car makes a left turn at 13 m/s. The (faulty) door will pop open at a force of 800 N. Supposing the same left turn but at a different speed, the least speed for which the passenger will get thrown out of the car is (a) 14 m/s (b) 19 m/s (c) 26 m/s (d) 36 m/s (e) 54 m/s

3 8. A 5.0 kg cart is moving across a frictionless horizontal surface at 6.0 m/s. In order to change its speed to 10 m/s, the minimum amount of work that must be done on the cart is (a) 40 J (b) 90 J (c) 160 J (d) 400 J (e) 500 J 9. A 1.5 kg crate falls from a height of 2.0 m onto a spring scale where the spring constant is N/m. Ignoring the small amount that the spring compresses when you calculate the gravitational potential energy, at the instant of maximum compression the scale reads (a) 15 N (b) 30 N (c) 1500 N (d) 2100 N (e) 3000 N 10. The diagram below shows a small ball of mass m = 0.45 kg attached to the end of a thin rod of length L = 0.5 m and negligible mass. The other end of the rod is pivoted so that the ball can move in a vertical circle. The rod is held horizontally, as shown, then given enough of a downward push so the ball can swing down and around, then reach the vertical position with zero speed there. The work that gravity did on the ball when it reaches its lowest point is (a) 2.2 J (b) 2.2 J (c) 4.4 J (d) 0.9 J (e) 0.9 J 11. The momentum of a particle is p = 5t 2 î 3 ĵ + 9t kˆ. The force as a function of time is (a) 5tî 3 ĵ + 9 kˆ (b) 10t î + 9 kˆ (c) 10tî 3 ĵ + 9 kˆ (d) 5t î + 9 kˆ (e) 10tî + 3 ĵ + 9t kˆ