Exam 3--PHYS 101--F15

Transcription

1 Name: Exam 3--PHYS 0--F5 Multiple Choice Identify the choice that best completes the statement or answers the question.. It takes 00 m to stop a car initially moving at 25.0 m/s. The distance required to stop the same car moving at 50.0 m/s under the same conditions is a. 00 m. b m. c m. d. 200 m. e. 400 m. 2. Consider this figure. A cart starts at point A with a speed of 4 m/s. What is the speed of the cart at point b? 4. Consider the figure in problem #2. A cart starts at point A with a speed of 4 m/s. Which of the following statements best describes the cart s energy at point (d). (Let the ground be h=0.) a. At point (d), PE=0 and KE=0. b. At point (d), PE>0 and KE=0. c. At point (d), PE=0 and KE>0. d. At point (d), PE>0 and KE>0. e. It depends on the mass of the cart. 5. By what factor does the kinetic energy of a car change if its velocity is doubled? a. b. 2 c. 4 d. 0.5 e a. 5 m/s b. 220 m/s c. 4.2 m/s d. 0. m/s e. 6 m/s 3. Consider the figure in the previous problem. A cart starts at point A with a speed of 4 m/s. If the cart comes to rest at point (e), what is the height at that point? a. 3 m b. 4.0 m c. 0. m d. 9.0 m e. m 6. Which of these statements is/are true? I. Conservative forces require contact between 2 objects. II. Field forces conserve energy. III. Friction is a conservative force. IV. Conservative forces are path-dependent. a. II only b. I, III, and IV c. II & IV d. all are true 7. A 0-kg toy car moving at 5.0 m/s hits an initially uncompressed horizontal spring with a spring constant of N/m. Neglecting the mass of the spring, the maximum compression of the spring is a..0 m. b. 0 m. c m. d. 2.0 m. e. 50 m.

2 8. A 0-kg toy car moving at 5.0 m/s hits an initially uncompressed horizontal spring with a spring constant of N/m. Neglecting the mass of the spring, what is the total elastic potential energy when the spring is completely compressed?. Consider this perfectly inelastic collision. What is the magnitude of the final velocity of the two particles? a. 200 J b. 50. J c. 3,000 J d. 500 J e. 30 J 9. A spring has a spring constant of 200 N/m. You apply a force of 600. N to compress the spring. By how much do you compress the spring? a m b..0 m c. 3.4 m d. 2.0 m e. 720,000 m 0. A machine gun is attached to a railroad flatcar that rolls with negligible friction. If the railroad car has a mass of kg, how many bullets of mass kg would have to be fired at 250 m/s off the back to give the railroad car a forward velocity of 0.5 m/s? a. 2 m/s b. 0.5 m/s c. 3.3 m/s d m/s e..5 m/s 2. An open cart rolls along a frictionless track while it is raining. As it rolls, what happens to the speed of the cart as the rain collects in it? (assume that the rain falls vertically into the box) a. speeds up b. maintains constant speed c. slows down d. stops immediately 3. A crane drops a 0.30 kg steel ball onto a steel plate. The ball's speed just before impact is 4.5 m/s; after impact, it rebounds at 4.2 m/s. If the ball is in contact with the plate for s, what is the magnitude of the average force that the ball exerts on the plate during impact? a. 3,000 b. 2,000 c. 5,000 d. 400 a. 3.5 N b. 87 N c. 33 N d. 3.0 N 2

3 4. A 0.0-kg ball is moving at 6 m/s when it is hit by a bat, causing it to reverse direction and have a speed of 4 m/s. What is the magnitude of the change in the momentum of the ball? a kg m/s b. 2.0 kg m/s c. 200 kg m/s d kg m/s 5. A uranium nucleus is at rest and undergoes fission and splits into two fragments, one heavy and one light. Which of these statements is true? a. the heavier fragment has a higher velocity than the light one b. the lighter and heavier fragments have the same momentum (but in opposite directions) c. the lighter fragment has more momentum than the heavy one d. the lighter and heavier fragments have the same velocity (but in opposite directions) 6. A force of 00 N acts on a 00 kg boulder for 2 seconds; the same force acts on a kg stone for 2 seconds. Which experiences the larger change in momentum? 7. Which of these bodies has the largest momentum? ( M represents mass; V represents velocity.) I. Mass 8M and speed V II. Mass M and speed 8V III. Mass 3M and speed 3V IV. Mass 2M and speed 3V a. I & II b. III alone c. IV alone d. III & IV e. II alone 8. If the momentum of an object is tripled, its kinetic energy will change by what factor? (Assume the mass of the object is unchanged.) a. zero b. one-third c. three d. nine 9. Which of these bodies has the largest energy? ( M represents mass; V represents velocity.) I. Mass 8M and speed V II. Mass M and speed 8V III. Mass 3M and speed 3V IV. Mass 2M and speed 3V a. I & II b. III alone c. IV alone d. III & IV e. II alone rev/min is equivalent to which of the following? a. 60 rad/s b rad/s c. 270 rad/s d. 43 rad/s a. the boulder b. the stone c. both the same 3

4 2. Between midnight and 3 am, the hour hand of a clock has what displacement? a. π 2 radians b. -45 degrees π c. 2 radians d. π radians e. π radians 22. The distance from the center of a Ferris wheel to a passenger seat is 2 m. What centripetal acceleration does a passenger experience when the wheel's angular speed is 0.50 rad/s? a. 3.0 m/s 2 b. 6.9 m/s 2 c. 6.0 m/s 2 d. 9.0 m/s A boy swings a 0.0 kg stone in a horizontal circle with a radius of 2.0 m. The string breaks under 80.0 N of tension. What is the maximum speed (in m/s) the stone can have? 24. A Ferris wheel, rotating initially at an angular speed of rad/s, accelerates over a 7.00 s interval at a rate of rad/s 2. What angular displacement does the Ferris wheel undergo in this 7.00 s interval? a rad b rad c rad d rad 25. Consider a point on a spinning wheel rotating with α = 0 rad. Which of these statements best s 2 describes the linear velocity of the point? a. the linear velocity is the same as the angular velocity b. the linear velocity does not change c. the linear velocity is changing constantly d. the linear velocity equals α 26. An object at rest begins to rotate with a constant angular acceleration. If this object rotates through an angle θ in the time t, through what angle did it rotate in the time /2 t? a. 6 m/s b. 4.0 m/s c. 400 m/s d m/s a. 4θ b. 2 θ c. 2θ d. 4 θ e. 3 4 θ 4

5 ID: A Exam 3--PHYS 0--F5 Answer Section MULTIPLE CHOICE. ANS: E PTS: REF: F5 2. ANS: A PTS: REF: F5 3. ANS: E PTS: REF: F5 4. ANS: D PTS: REF: F5 5. ANS: C PTS: REF: F5 6. ANS: A PTS: REF: F5 7. ANS: A PTS: 0 REF: F5 8. ANS: E PTS: 0 REF: F5 9. ANS: A PTS: 0 REF: F5 0. ANS: C PTS: REF: F5. ANS: D PTS: REF: F5 2. ANS: C PTS: REF: F5 3. ANS: B PTS: REF: F5 4. ANS: B PTS: REF: F5 5. ANS: B PTS: REF: F5 6. ANS: C PTS: REF: F5 7. ANS: B PTS: REF: F5 8. ANS: D PTS: REF: F5 9. ANS: E PTS: REF: F5 20. ANS: C PTS: REF: F5 2. ANS: A PTS: REF: F5 22. ANS: A PTS: REF: F5 23. ANS: B PTS: REF: F5 24. ANS: D PTS: REF: F5 25. ANS: C PTS: REF: F5 26. ANS: D PTS: REF: F5