Exam 2--PHYS 101--F17

Transcription

1 Name: Exam 2--PHYS 0--F7 Multiple Choice Identify the choice that best completes the statement or answers the question.. A ball is thrown in the air at an angle of 30 to the ground, with an initial speed of 40 m/s. How long will it take to reach its maximum height? 4. Two shells are fired simultaneously from the same battleship at two targets. The shells follow the trajectories shown here. Which of the following statements about the shells trajectory must be true? a. 4 s b. 6 s c. 2 s d. 8 s e. s 2. What is the horizontal range of the ball in the previous problem? I. They have different angles. II. They have different initial speeds. III. Shell # is in flight for more time than shell #2. a. I & III b. I and II c. I, II, and III d. I only e. III only a. 40 m b. 80 m c. 40 m d. 60 m 3. For the previous two problems, what is the x-component of the initial velocity? a. 20 m/s b. 0 m/s c. 35 m/s d. 40 m/s 5. For the two-dimensional motion of a projectile that begins and ends at the same height, all of the following apply except a. the y-component of the velocity changes direction during flight b. the y-component of the acceleration is always negative c. the maximum speed is at the top of the trajectory d. the time in flight is determined by the y-component of the velocity

2 6. You hit a ball horizontally from the top of a cliff that is 20 m tall. The ball has an initial velocity of 5 m/s. What is the horizontal range of the ball? a. 0 m b. 20 m c. 40 m d. 00 m e. 200 m 7. Which of these plots represents the y-position for an object launched horizontally from the top of a cliff. Then, the object proceeds until it lands at some distance from the bottom of the cliff. a. a b. b c. c d. d e. none of these 8. You drop a package from a plane flying at constant speed in a straight line. Without air resistance, the package will: a. quickly lag behind the plane while falling b. remain vertically under the plane while falling c. move ahead of the plane while falling d. not fall at all 9. From the same height (and at the same time), one ball is dropped and another ball is fired horizontally. Which will hit the ground first? a. the fired ball b. the dropped ball c. they both hit at the same time d. it depends on how hard the ball was fired e. it depends on the initial height of the balls 0. Which of these statements is true for an object in projectile motion? I. The x-component of the velocity does not change. II. The y-component of the velocity is zero at the top of the trajectory. III. The velocity is greatest at the beginning of the trajectory. IV. The acceleration in the y-direction at the top of the trajectory is zero. a. I, II, and III b. I, II, and IV c. II, III, and IV d. I & II e. all of these are true. You fire a ball with an initial speed of 20 m/s at an angle of 30º from the horizontal. It lands on a table, 26 meters from the original position, at t=.5s. What is the height of this table? a. 20 m b. 7 m c. 8 m d. 4 m e. 30 m 2

3 2. Two objects, A and B, experience the same acceleration. However, object A has twice the mass of object B. Therefore,... a. the force on object A is twice the force on object B b. the force on object A is four times the force on object B c. the force on object A is the same as the force on object B d. the force on object A is one-half the force on object B e. the force on object A is one-quarter the force on object B 3. Which is larger: I. the gravitational force exerted by the Earth on the Moon II. the gravitational force exerted by the Moon on the Earth a. I b. II c. I & II are the same d. it depends on the distance between them at that particular time 4. An object slides to the right on a horizontal surface. Which of these statements about the frictional force is true? I. The frictional force is to the left. II. The frictional force is only dependent on the weight of the object. III. The frictional force would decrease if the mass of the object was less. IV. The frictional force is dependent on the speed of the object. a. I & II b. I, II, and III c. I only d. II & IV e. I & III 5. A hockey puck slides on ice at constant velocity. What is the net force acting on the puck? a. zero b. depends on the speed of the puck c. more than its weight d. less than its weight but more than zero e. equal to its weight 6. Antilock breaks keep the car wheels from locking up when you stop your car. Why does this help slow the car down? a. µ k > µ s so static friction is better b. µ k > µ s so sliding friction is better c. µ s > µ k so static friction is better d. µ s > µ k so sliding friction is better 7. You push an object of mass M with a force F and cause the object to reach a speed v in a certain time. If you apply the same force to an object with mass M, what velocity does it reach in that same 2 time? a. 2v b. 2 v c. v d. 4 v e. 4 v 8. You put your book on the bus seat next to you. When the bus stops suddenly, the book slides forward off the seat. Why? a. a net force acted on it b. no net force acted on it c. it remained at rest d. it did not move, but only seemed to e. gravity briefly stopped acting on it 3

4 9. A block with mass 2.0 kg moves on a flat surface. A force of 0.0 N causes the block to move with an acceleration of 2.0 m/s 2. What is the coefficient of kinetic friction? 23. A 200 kg boat moves through the water with two forces acting on it. One is a 000 N forward push by the water on the propellor, and the other is a 600 N resistive force due to the water on the bow. If the boat starts at rest and travels for 0 seconds, what is its velocity? a. 0.4 b. 0.5 c. 0. d. 0.2 e A woman who weighs 700 N steps onto a scale that is in an elevator. The elevator begins to accelerate. The woman now weighs 500 N (according to the scale). The acceleration of the elevator is a. 0 m/s b. 6 m/s c. 3 m/s d. 20 m/s e. 5 m/s 24. Consider this figure. The block is accelerating down the inclined plane; the block does experience a force due to kinetic friction. Which of the following equations is correct? a. 2.9 m/s 2 downward b. 9.8 m/s 2 downward c. 7 m/s 2 upward d. 7 m/s 2 downward e. 3 m/s 2 upward 2. How much tension is needed to lift a 000 kg elevator upward with an acceleration of 2 m/s 2? a. 2,000 N b. 8,000 N c. 5,000 N d. 0,000 N 22. A 20 kg object moves from left to right at a speed of 3 km/h. What net force is required to keep this object moving in a straight line at constant speed? a. 0 N b. 0.2 N c. 60 N d. 7 N a. I, II, and III b. II & III c. I & II d. II only e. none are correct I. F N F w sin 60 = 0 II. f k F w cos 30 = ma x III. F N F w = 0 4

5 25. In this figure, the block has a mass of kg and sits on an incline plane with an angle θ=30. If there is no friction, what is the acceleration of the block down the inclined plane? a. 5 m/s 2 b. 0 m/s 2 c. 00 m/s 2 d. 20 m/s 2 e. 9 m/s Consider the previous problem. If the coefficient of kinetic friction between the block and plane is 0.2, what is the acceleration of the block down the plane? a. 3 m/s 2 b. 6 m/s 2 c. m/s 2 d. 4 m/s 2 e. the block doesn t move 27. Consider the previous problem. What is the normal force acting on the block? a. 7 N b. 5 N c. 9 N d. 0 N 28. Who can do well in this course? a. Joe Thibodaux b. The lady next to me c. Jenny Gauthreaux d. Me!!!! 5

6 ID: A Exam 2--PHYS 0--F7 Answer Section MULTIPLE CHOICE. ANS: C PTS: REF: F7-OXT 2. ANS: A PTS: REF: F7 3. ANS: C PTS: REF: F7 4. ANS: D PTS: REF: F7 5. ANS: C PTS: 0 REF: F7 6. ANS: A PTS: REF: F7 7. ANS: C PTS: REF: F7 8. ANS: B PTS: REF: F7 9. ANS: C PTS: REF: F7 0. ANS: A PTS: REF: F7. ANS: D PTS: REF: F7 2. ANS: A PTS: REF: F7 3. ANS: C PTS: REF: F7 4. ANS: E PTS: REF: F7 5. ANS: A PTS: REF: F7 6. ANS: C PTS: REF: F7 7. ANS: A PTS: REF: F7 8. ANS: B PTS: REF: F7 9. ANS: E PTS: REF: F7 20. ANS: A PTS: REF: F7 2. ANS: A PTS: REF: F7-OXT 22. ANS: A PTS: REF: F7-OXT 23. ANS: D PTS: REF: F7-HW 24. ANS: E PTS: REF: F7 25. ANS: A PTS: REF: F7 26. ANS: D PTS: REF: F7 27. ANS: C PTS: REF: F7 28. ANS: D PTS: