Physics 2A Final ExaminationName _______________________________________________________________________ Signature ____________________________________________________________________ Student ID Number____________________________________________________________ • By signing this exam, you affirm that you are the person named on this exam with this student ID. You also agree to abide with the Academic Integrity Policy, as outlined in the course introduction and the UCR General Catalog. • You have 3 hours to answer 39 multiple-choice questions. There are 26 conceptual questions worth 1 point each and 13 quantitative questions worth 2 points each. • This is a closed-book exam and thus no books or notes are allowed. There is a formula sheet on the last page (which you may remove). If you need scratch paper, there is some at the front of the lecture hall. • You may use a calculator, provided no information is programmed into it. • Remember to put your name and student ID number on the Scantron. It is critical to “bubble in” your student ID. Failure to do so may result in no credit! • When you are finished, or at the end of the 3 hours, turn in this exam along with your Scantron, which has your student ID bubbled in. PHYS 2A Final Exam Fall 2014 1 Instead. C) Since the ground is stationary. 1. If we repeat this experiment with a box of mass 2m A) the lighter box will go twice as high up the incline as the heavier box. What is the reason for using a long barrel in these guns? A) to allow the force of the expanding gases from the gunpowder to act for a longer time B) to reduce the force exerted on the bullet due to the expanding gases from the gunpowder C) to increase the force exerted on the bullet due to the expanding gases from the gunpowder D) to reduce frictional losses 1 . After it is released. D) just as it moves free of the spring. Which of the following is the most accurate statement? A) When you push down on the earth with a force greater than your weight. 2. Choose the one alternative that best completes the statement or answers the question. E) both boxes will reach the same maximum height on the incline. Bubble in your answer on your SCANTRON form. D) It is the upward force exerted by the ground that pushes you up. the lighter box will be moving twice as fast as the heavier box. A box of mass m is pressed against (but is not attached to) an ideal spring of force constant k and negligible mass. C) just as it moves free of the spring. it is the internal forces of your muscles acting on your body itself which propels the body into the air. the earth will push back with the same magnitude force and thus propel you into the air. but this force can never exceed your weight. the box slides up a frictionless incline as shown in the figure and eventually stops. During World War I.1 point each MULTIPLE CHOICE. compressing the spring a distance x. This gun also had a long barrel. the heavier box will have twice as much kinetic energy as the lighter box. 3.Conceptual Questions . Consider what happens when you jump up in the air. B) both boxes will have the same speed just as they move free of the spring. B) You are able to spring up because the earth exerts a force upward on you which is stronger than the downward force you exert on the earth. it cannot exert the upward force necessary to propel you into the air. Germany used a "Big Bertha" cannon to hurl shells into Paris 30 miles away. at a constant speed. when is the magnitude of the acceleration the highest? A) It is highest at the top of its trajectory. car M. B) Car M C) Car L D) Car N 2 . C) Yes. for which car is the amount of work done by friction in stopping it the highest? A) The amount of work done by friction is the same for all cars. B) No. gravity. since the choice of the zero of potential energy is arbitrary. Three cars (car L. C) The acceleration of the object is the same throughout the entire trajectory. A string is attached to the rear-view mirror of a car. Suppose the force of wind resistance is proportional to the speed of the object and in the direction opposite the object's velocity. This track has markers spaced at equal distances along it from the start. The car is driving around in a circle. as long as the total energy is positive. and the centripetal force C) tension D) tension and gravity 7. The car reaches a speed of 140 km/h as it passes marker 2. at 70 km/h? A) before marker 1 B) at marker 1 C) between marker 1 and marker 2 5. as shown below. B) It is highest right after the object is released. Which of the following lists gives all of the forces directly acting on the ball? A) tension. and the least massive is car N. A racing car accelerates uniformly from rest along a straight track. Assuming all three cars have identical tires. and friction B) tension. If you throw an object upward.e. and slam on the brakes. A ball is hanging on the other end of the string. Whereabouts on the track was the car when it was travelling at half this speed. because this would have no physical meaning. as long as the kinetic energy is positive. The most massive car is car L. the centripetal force. 6. gravity. and car N) are moving with the same velocity. D) No. because the kinetic energy of a system must equal its potential energy. i.4. 8. Is it possible for a system to have negative potential energy? A) Yes. E) Yes. it cannot exert any force on the man. immovable wall. D) The velocity depends on the radius of the tire. without slipping. C) v. E) The friction force on the man's feet is directed to the left.8 N. the top string segment will break. it's velocity with respect to the road is A) 1. A number of 6-kg weights are hung one below the other from a hook in the ceiling using this string. Which of the following is the most accurate statement concerning this situation? A) If the man pushes on the wall with a force of 200 N. and there is no limit to the number of weights that can be suspended.5 v. 10. all string segments will break. all string segments will break. 3 . C) Each segment has a tension of 58. the bottom string segment will break. E) When the 67th weight is added. D) When the 7th weight is added. The number of weights that causes the string to break and the string segment that will break are as follows: A) When the 7th weight is added. 11. with a velocity v. B) Since the wall cannot move. A man pushes against a rigid. In the figure. A piece of tape is attached to the tire. C) The man can never exert a force on the wall that exceeds his weight.9. B) 2 v. A tire is rolling along a road. When the tape is opposite the road (at the top of the tire). D) The man cannot be in equilibrium since he is exerting a net force on the wall. we can be sure that the wall is pushing back with a force of exactly 200 N on him. B) When the 7th weight is added. a certain type of string will break if the tension in the string exceeds 400 N. If the planet had half as much mass. The brick is now flipped so that a face of smaller area is in contact. A brick initially has its largest-area face in contact with a rough surface. A person ties a rock to a string and whirls it around in a vertical circle such that sometimes the rock is going straight upward and sometimes the rock is going straight down. A satellite having orbital speed V orbits a planet of mass M. 15. What force is now required to pull the brick along at constant speed as before? A) a smaller force B) the same force C) a greater force D) One cannot say without knowing the coefficient of friction. The material of the brick is uniform on all faces. due to the force exerted on it by another particle. as on the right in the figure. as shown on the left in the figure. the orbital speed of the satellite would be: A) V B) V/ 2 C) 2V 4 D) V/2 E) V 2 . 14. A force F is required to pull the brick along the surface at constant speed. C) It is highest when the rock is at the lowest elevation. At which of the three points labeled in the figure is the magnitude of the force on the particle greatest? A) point X B) point Y C) point Z 13. as a function of distance. The plot in the figure shows the potential energy of a particle. B) The tension is constant as the rock moves around in a circle. When is the tension the highest? A) It is highest when the rock is at the highest elevation. She whirls the rock at the minimum speed (constant in time) such that the string is always taut (no sag).12. A 5 kg ball collides head-on with a 10 kg ball. A girl throws a stone from a bridge.16. D) The magnitude of the change of velocity the 5 kg ball experiences is equal to that of the 10 kg ball. After they are released and have both moved free of the spring A) the heavier block will have more kinetic energy than the lighter block. 18. B) the magnitude of the momentum of the heavier block will be greater than the magnitude of the momentum of the lighter block. E) both blocks will both have the same amount of kinetic energy. The speed of the stone as it leaves her hand is the same in each case. The collision is inelastic. They are not attached to the spring. B) The magnitude of the change of the momentum of the 5 kg ball is equal to the magnitude of the change of momentum of the 10 kg ball. the net gravitational force exerted on the astronaut by these two objects would be A) zero. In which case will the speed of the stone be greatest when it hits the water below? A) Case A B) Case B C) Case C D) Case D E) The speed will be the same in all cases. B) the truck exerts a smaller amount of force on the cyclist than the cyclist exerts on the truck. Case A: Thrown straight up. Case B: Thrown straight down. During the collision A) the truck exerts a greater amount of force on the cyclist than the cyclist exerts on the truck.0-kg block are pressed together on a horizontal frictionless surface with a compressed very light spring between them. C) The magnitude of the change of velocity the 5 kg ball experiences is less than that of the 10 kg ball. If an astronaut were exactly halfway between the Earth and the Moon. Which statement is true? A) The magnitude of the change of velocity the 5 kg ball experiences is greater than that of the 10 kg ball. 20. and air resistance is negligible. C) the truck exerts the same amount of force on the cyclist as the cyclist exerts on the truck. 5 . E) Two of the above statements are true. Case C: Thrown out at an angle of 45° above horizontal. Consider the following ways she might throw the stone. A large truck collides head-on with a cyclist. D) both blocks will have equal speeds. Case D: Thrown straight out horizontally. B) directed towards the Moon.0-kg block and a 2. 17. D) the truck exerts a force on the cyclist. A 1. C) the lighter block will have more kinetic energy than the heavier block. 19. C) directed towards Earth. which is initially stationary. but the cyclist exerts no force onto the truck. D) its velocity is perpendicular to the acceleration. Swimmers at a water park have a choice of two frictionless water slides as shown in the figure. B) the horizontal and vertical components of its velocity are zero. Ignoring friction. each of the same mass and uniform thickness. 6 . both objects are moving at the same speed. An object slides into a spring. E) its velocity and acceleration are both zero. For general projectile motion. C) its acceleration is zero. dropping quickly at first and then leveling out. A) momentum and potential energy B) momentum and kinetic energy C) momentum and mechanical energy D) kinetic energy only E) momentum only 22. When the spring is most compressed. 24. 23. what is conserved during this interaction. How does the speed v1 of a swimmer reaching the end of slide 1 compares with v2.21. the speed of a swimmer reaching the end of slide 2? A) v1 = v2 B) v1 < v2 C) v1 > v2 D) No simple relationship exists between v1 and v2 because we do not know the curvature of slide 2. Although both slides drop over the same height. Which has the greatest moment of inertia when rotated about an axis perpendicular to the plane of the drawing? In each case the axis passes through point P. A) D B) A C) B D) C E) The moment of inertia is the same for all of these objects. slide 1 is straight while slide 2 is curved. h. which is attached to another mass that is initially stationary. In the figure are scale drawings of four objects. when the projectile is at the highest point of its trajectory A) the horizontal component of its velocity is zero. the dog A) moves to the right. The tail bed is coated with ice. and then accelerates to the right. B) moves to the left. In the figure.25. The masses of the blocks. moving along a flat road. 7 . D) not possible because momentum is not conserved. and the velocities before and after are given. determine the character of the collision. The truck is initially at rest. but the back of the truck moves towards the dog. D) moves to the right at the same rate as the truck. C) does not move left or right. as the truck moves to the right. The collision is: A) partially inelastic. causing the dog to slide towards the back of the truck. 26. B) completely inelastic. C) perfectly elastic. but not as quickly as the truck is moving to the right. so it doesn't slide. As seen from a stationary observer (watching the truck move to the right). causing it to slide towards the back of the truck. A dog is standing in the tail bed of a pickup truck. causing the force of friction between the dog and the truck to be zero. and the block is projected with a velocity v1 = 1.2 points each 27. The external force is removed.0-kg bucket of concrete from the ground up to the top of a 40.41 m/s 28.36 N 29. A 425 kg car moving at 17. but is traveling at 4.Quantitative Questions . D) 1100 N/m. where it stops.98 m/s D) 3.8 m/s2. E) 3900 N/m. extending to E. The block descends a ramp and has a velocity v2 = 1.6 m/s hits from behind another car moving at 9. what is the velocity of the first car after the collision? A) -3.4 m/s at C.8 m/s C) 9. If the second car has a mass of 580 kg and a new speed of 19. An 0.39. B) 1600 N/m.84 kJ 8 .9 m/s at the bottom.2 m/s upon separation from the spring.41 m/s B) 31. 30. The track is frictionless between points A and B.4 m/s in the same direction. what is the magnitude of the upward force on the skydiver due to wind resistance? (Use g = 9.00 kJ E) 7.8 m/s. If the skydiver has a mass of 72. What is the minimum amount of work that the worker did in lifting the bucket? A) 960 J B) 800 J C) 160 J D) 8. The spring constant of the spring is closest to A) 2000 N/m. The block enters a rough section at B.0-m tall building. The velocity of the block is v3 = 1. A skydiver reaches a "terminal velocity" of 120 km/h. C) 2600 N/m.62 N B) 778 N C) 707 N D) 7.) A) 6. The coefficient of kinetic friction over this section is 0. A worker lifts a 20.1 kg. The bucket is initially at rest. The block moves on to D.80-kg block is held in place against the spring by a 67-N horizontal external force (see the figure).0 m/s when it reaches the top of the building. 31. C) 900 m/s.6-m down the incline. An 8. .5 m/s2 D) 8.0 kg block when the other block is released? (See the figure.80 s. A 10. what is the magnitude of acceleration of the 10. An 8. The initial velocity of the bullet is closest to A) 1300 m/s. E) 1100 m/s.00 m/s. How much work does gravity do on the block during this process? A) +81 J B) +120 J C) +100 J D) -100 J E) -81 J 32.0 m/s2 C) 7. Assuming that frictional forces may be neglected. which is hanging over the edge of the table. with v1 = 0. as shown in the figure. in a time interval of 0. at rest on a frictionless horizontal surface (see the figure). The spring constant of the spring is 2400 N/m. The block moves a distance of 1.5 m/s2 B) 9.0 m/s. on a rough incline.) A) 8. The block moves into an ideal massless spring and compresses it by 8. and acquires a velocity of v2 = 4.1 m/s2 33. The bullet remains lodged in the block.0-kg block. 9 D) 1200 m/s.7 cm.0 kg block on a table is connected by a string to a 63 kg mass. B) 1000 m/s.0-g bullet is shot into a 4.0-kg block is released from rest. 9 cm below the starting point.5 rad/s2 until the wheel stops. If instead of having been lowered slowly the object was dropped from rest. If each time it loses 20. A uniform sign is supported at P as shown in the figure.0 m from the floor? A) 100 cm B) 10 cm C) 130 cm D) 100 mm 38. and begin rotating about each other. a distance of 7. What is their angular speed? A) 6.0 rad/s C) 8. the angular acceleration of the wheel between t = 0 s and t = 10 s is closest to: A) 10 rad/s2 B) 8.6 m apart. Two ice skaters of identical mass approach on parallel paths 1.9 cm C) 11 cm D) 22 cm E) 16 cm 39.3 rad/s B) 5. If the sign is a square 0.6 rad/s2 C) 13 rad/s2 D) 12 rad/s2 36.42 m/s2. what is the magnitude of the horizontal force that P experiences? A) 25 N B) 20 N C) 0 N D) 61 N 35. how high does it rise after the third bounce.34. The wheel slows down uniformly at 2.8 m on its side and its mass is 5.0 m/s. The wheel is run at that angular velocity for 27 s and then power is shut off. at time t = 0 s.0 rad/s 10 . Both are moving at 5.6 m separation.0 kg. maintaining their 1. how far then would it then stretch the spring at maximum elongation? A) 32 cm B) 7. It takes 4700 N to accelerate a car at a rate of 3. The wheel accelerates uniformly for 10 s and reaches the operating angular velocity of 72 rad/s. They join hands as they pass. A machinist turns the power on to a grinding wheel. An object is attached to a hanging unstretched ideal and massless spring and slowly lowered to its equilibrium position. A tennis ball bounces on the floor three times. In this situation.0% of its energy due to heating.0 rad/s D) 4. What is the mass of the car? A) 1580 kg B) 1370 kg C) 1040 kg E) 7. at rest. provided we released it 2.2 rad/s2 D) 1780 kg 37. . Static Friction: f s 7. vt 0. ( Fnet ) z at 0 r . Drag D s dp . Newton’s Laws of Motion Fi 5. 11. ( Fnet ) t mrvt mn rn2 I n f 12. Vectors A Ax iˆ A B Ay ˆj A cos Ax AB cos Ax B x A sin Ay Ay B y A B 2nd Fnet 4. Apparent Weight wapp 6. Relation Between Rotational and Translational Quantities s 10. Uniform Circular Motion p. Moment of Inertia dL dt I g Kinetic Friction: f k Av 2 where r Ax FBA 8. Kinematic Equations (constant acceleration) Translational v fs vis a s t sf sf Rotational si f f vis t as ( t ) 2 1 2 v 2fs t i i i si vis2 f t ( t)2 1 2 1 2 v fs ) t 2a s ( s f 1 2 i 2 f (vis 2 i ( i si ) f 2 ( ) t f i ) 3. dt ma net k n Rolling Friction: f r r n ~ 14 kg/m 3 9. Impulse-Momentum Theorem Fs (t )dt Js i ps r . Torque Ay tan ay w1 n Ay2 AB sin i 3rd FAB Ax2 A ( Fnet ) r mvt2 r mr 2 . r .) f f dv s ds as vs s f si v s dt v fs vis a s dt dt dt i i d dt d dt 2.Physics 2A – Final Exam Formula Sheet (Vectors are denoted with arrows above the symbols) 1. Velocity and Acceleration (s represents position along a generic axis. Kinetic Energy Angular: L 1 2 Gm1 m2 r2 F mv 2 dU dx Ug Gravitational (y << r): Elastic: U s mgy 19. Mathematics dE sys dt 25. Work W Work from a Constant Force Fs ds W F r i 21. Constants Lf F v If ax 2 Law of Cosines: C 2 K U Pf Conservation of angular momentum: Li 23.Linear: p 13. Hooke’s Law mv K 18. 22. Momentum 1 M rCM 14.67x10-11Nm2/kg2 sin A sin B . and Wext is the work done by external forces. L mrvt I mn rn n k s 16. Perfectly Elastic Collisions ( vi 2 1 2 k ( s) 2 Gm1 m2 r Gravitational (y ~ r): U g 0) vf1 m1 m1 m2 vi1 . Wdiss Eth is the work done by dissipative forces.8 m/s2. Potential Energy Fx r p. Center of Mass ( Fsp ) s 15. B2 0 then x 2 AB cos b b2 2a 4ac Law of Sines: G = 6. Conservation Laws for an Isolated System E sys Conservation of energy: E mech Conservation of linear momentum: Pi Eth P 24. Newton’s Law of Gravity 17. Work-Kinetic Energy Theorem K Wnet Wc Wdiss Wext where Wc U is the work done by the conservative forces. Power 0 where E mech bx c A2 g = 9. m2 2m1 vi1 m1 m2 vf2 f 20.