1) < 0, 6, 8 > J 2) < 0, 3, 4 > J 3) 2 J 4) 10 J 5) 25 J

Transcription

1 Q6.2.a: A ball whose mass is 2 kg travels at a velocity of < 0, 3, 4> m/s. What is the kinetic energy of the ball? 1) < 0, 6, 8 > J 2) < 0, 3, 4 > J 3) 2 J 4) 10 J 5) 25 J

2 Q6.2.aa: A ball whose mass is 2 kg travels at a velocity of < 0, 3, 4> m/s. What is the kinetic energy of the ball? 1) 0 J 2) 2 J 3) 10 J 4) 25 J 5) < 0, 9, 16 > J

3 Q6.2.b: A ball whose mass is 2 kg travels at a velocity of < 0, 3, 4> m/s. What is the rest energy of the ball? 1) 0 J 2) 25 J 3) 6e8 J 4) 9e16 J 5) 1.8e17 J

4 Q6.2.c: Consider an electron (mass 9e-31 kg) moving with speed v = 0.9c. What is its rest energy? 1) 7.3e-31 J 2) 8.1e-14 J 3) 1.05e-13 J 4) 1.86e-13 J 5) 2.7e8 m/s

5 Q6.2.d: Consider an electron (mass 9e-31 kg) moving with speed v = 0.9c. What is its total (particle) energy? 1) 7.3e-31 J 2) 8.1e-14 J 3) 1.05e-13 J 4) 1.86e-13 J 5) 2.7e8 m/s

6 Q6.2.e: Consider an electron (mass 9e-31 kg) moving with speed v = 0.9c. Its rest energy is 0.81e-13 J, and its (total) particle energy is 1.86e-13 J. What is its kinetic energy? 1) 7.3e-31 J 2) 3.28e-14 J 3) 8.1e-14 J 4) 1.05`e-13 J 5) 1.86e-13 J

7 Q6.3.a: On a space station, you pushed a box that was initially floating at rest at location < 0, 0, 10 > m to location < 0, 0, 14 > m, applying a force < 0, 0, 5 > N. How much work did you do on the box? 1) W = 20 J 2) W = 50 J 3) W = 70 J 4) W = 140 J 5) Not enough information

8 Q6.3.b: You did 20 J of work on the box. What happened? 1) The box slowed down. 2) The box speeded up. 3) The box moved at constant speed.

9 Q6.3.c: You apply a force of < 0, 0, 5 > N to a box for 3 seconds. How much work did you do on the box? 1) W = 15 J 2) W = 5 J 3) W = 3 J 4) W = 5/3 J 5) Not enough information. Q6.3.d

10 A figure skater slides in the x direction along the ice, toward her partner. When she gets close he pushes on her in the +x direction, to slow her down. Does he do positive, negative, or zero work? 1) positive 2) negative 3) zero r F

11 Q6.3.e A fancart moves in the x direction. The fan is on, and the force on the cart by the air is also in the x direction. Is the work done by the air positive, negative, or zero? r 1) positive 2) negative 3) zero F

12 Q6.3.f A skater on a skateboard coasts in the +x direction. He is about to run into his friend, so she pushes him in the x direction, to slow him down. What is the sign of the work done by the friend? F r 1) positive 2) negative 3) zero

13 Q6.3.g: A tennis ball is moving in the y direction. You hit it downward with a tennis racket. During the time your racket is in contact with the ball, do you do positive, negative, or zero work on the ball? F r 1) positive 2) negative 3) zero

14 Q6.3.h You move an object from < 3, 7, 4 > m to < 2, 10, 12 > m, applying a force < 10, 20, 30 > N How much work do you do? 1) 10 J 2) 170 J 3) < -10, -60, 240 > J 4) < 30, -140, 120 > J 5) ( 10 ) 2 + ( 60) 2 + ( 240 ) 2 J

15 Q6.3.i You drop a ball of mass m at a height h above the ground. The ball falls, speeding up, bounces off the floor, and goes upward, slowing down, until it is once again at the location where you released it (height h). Initial state: Just after release Final state: Ball back at original location How much work was done by the Earth on the ball? 1) mgh 2) mgh 3) 2*mgh 4) 2*mgh 5) 0

16 + Q6.5.a: An isolated neutron decays: n p + e + ν + Initial: Neutron at rest Final: p, e, and ν far from each other 1) The sum of the rest energies of the products equals the rest energy of the neutron 2) The sum of the kinetic energies of the products equals the rest energy of the neutron 3) The sum of the rest energies and kinetic energies of the products equals the rest energy of the neutron 4) The sum of the kinetic energies of the products equals the kinetic energy of the neutron

17 + Q6.5.b: An isolated neutron decays: n p + e + ν Initial: Neutron at rest + Final: p, e, and ν far from each other System: All particles Energy principle: Ef = Ei + W What quantities are included in the initial energy Ei? A: Kn C: Ke E: mnc 2 G: mec 2 B: Kp D: Kν F: mpc 2 H: mνc 2 1) A 2) A, E 3) A, B, C, D 4) E, F, G, H 5) A, F, G, H

18 + Q6.5.c: An isolated neutron decays: n p + e + ν Initial: Neutron at rest + Final: p, e, and ν far from each other System: All particles Energy principle: Ef = Ei + W What quantities are included in the final energy Ef? A: Kn C: Ke E: mnc 2 G: mec 2 B: Kp D: Kν F: mpc 2 H: mνc 2 1) A, C, E, G 2) B, C, D, F, G, H 3) A, E 4) B, C, D 5) E, F, G

19 Q6.7.a: You push a crate out of a carpeted room and along a tiled hallway. While on the carpet you exert a force of 30 N and the crate moves 2 m. While on the tile you exert a force of 12 N and the crate moves 8 m. How much work do you do? 1) 210 J 2) 180 J 3) 156 J 4) 105 J 5) 42 J 6) We need to know the mass of the crate.

20 Q6.7.b A horizontal spring has stiffness 100 N/m. A block is pressed against the spring, compressing the spring 0.2 m, and then released. When the spring has reached its relaxed length, how much work will it have done on the block? 1) 20 J 2) 4 J 3) 2 J 4) 0 J 5) We need to know the mass of the block

21 Q6.8.a A thrown ball heads straight up. SYSTEM: Ball What is the work done by the surroundings? 1) 0 2) mg y 3) mg y 4) something else

22 Q6.8.b A thrown ball heads straight up. SYSTEM: Ball + Earth What is the work done by the surroundings? 1) 0 2) mg y 3) mg y 4) something else

23 Q6.8.c A thrown ball heads straight up. SYSTEM: Ball + Earth How did the kinetic energy of the system change? 1) K > 0 2) K = 0 3) K < 0

24 Q6.8.d A ball of mass 0.1 kg is dropped from rest near the Earth. The ball travels downward 2 m, speeding up. SYSTEM: Ball What is the work done by the surroundings? 1) 0 2) J 3) 1.96 J

25 Q6.8.e A ball of mass 0.1 kg is dropped from rest near the Earth. The ball travels downward 2 m, speeding up. SYSTEM: Ball + Earth What is the work done by the surroundings? 1) 0 2) J 3) 1.96 J

26 Q6.8.f A ball of mass 0.1 kg is dropped from rest near the Earth. The ball travels downward 2 m, speeding up. SYSTEM: Ball + Earth Work done by surroundings: 0 However, did the kinetic energy of the Ball + Earth system change? 1) K increased 2) K decreased 3) K did not change

27 For the system of Ball + Earth, K > 0 but W = 0. We have a problem...

28 Q6.9.a A spacecraft travels from near the Earth toward the Moon. How many gravitational potential energy terms Ug are there in the Energy Principle? System: Earth, Moon, spacecraft 1) 1 2) 2 3) 3 4) 6 5) 0

29 Q6.11.a: Which of the following graphs of U vs r represents the gravitational potential energy, U = GMm/r?

30 Q6.11.b: In which graph does the cyan line correctly represent the sum of kinetic energy plus potential energy? 1) A 2) B 3) C

31 Q6.12.a A comet orbits a star in a strongly elliptical orbit. The comet and star are far from other massive objects. System: comet + star The system has: 1) kinetic energy 2) kinetic energy and rest energy 3) kinetic energy, rest energy, and potential energy

32 Q6.12.b System: comet + star As the comet travels away from the star, how does the kinetic energy and potential energy of the system change? K U 1) increase decrease 2) increase increase 3) decrease increase 4) decrease decrease 5) no change no change

33 Q6.12.c: A robot spacecraft leaves an asteroid. SYSTEM: craft + asteroid Which quantities are the same in the initial state and the final state (that is, which quantities do not change significantly, for this system)? 1) rest energy of asteroid, rest energy of spacecraft 2) rest energy of asteroid, rest energy of spacecraft, and kinetic energy of asteroid 3) rest energy of asteroid, rest energy of spacecraft, and gravitational potential energy 4) rest energy of asteroid, rest energy of spacecraft, and kinetic energy of asteroid, and gravitational potential energy

34 Q6.12.d: The system is a comet and a star. In which case(s) will the comet escape from the star and never return? 1) A 2) B 3) C 4) A,B 5) B,C 6) A,B,C

35 Q6.14.a Jack pulls to the left on a positive charge, while Jill pulls to the right on a negative charge. System: both charges Which forces are external? 1) F1 and F2 2) F2 and F3 3) F3 and F4 4) F1 and F4

36 Q6.14.b The charges are displaced, then remain at rest. System: both charges The work done by external forces was: 1) positive 2) negative 3) zero 4) need more information

37 Q6.14.c System: both charges Initial state: charges at rest Final state: charges at rest, farther apart The positive work done by external forces: 1) increased K of the system 2) decreased K of the system 3) did not change K of the system

38 Q6.14.d y-axis: energy; x-axis: separation Which graph correctly shows U for a proton and an electron? 5: none of the above

39 Q6.14.e y-axis: energy; x-axis: separation Which graph correctly shows U for two interacting protons? 5: none of the above

40 Q6.14.f Two electrons, initially far apart, heading toward each other. Same initial speed v. How close do they get before stopping? K1f + K2f + Uf = K1i + K2i + Ui + W Which terms are NOT zero? 1) K1f, K2f 2) Uf 3) K1i, K2i 4) Ui 5)K1f, K2f, Ui 6) K1i, K2i, Uf

41 Q6.14.g Two electrons, initially far apart, heading toward each other. By applying the energy principle we found that: Uf = K1,i + K2,i Which term contains the distance of closest approach? 1) Uel,f 2) K1,i 3)K2,i 4) None of the above

42 Q6.14.h y-axis: energy; x-axis: separation Which graph shows K, U, and K+U for the two interacting electrons? 5: none of the above

43 Q6.17.a: alpha + carbon => oxygen + photon What is the minimum initial kinetic energy of the alpha particle? moc 2 + KO + Eγ = m α c 2 + mcc 2 + K α + Kc + Ui Which term contains the unknown?

44 Q6.17.b: alpha + carbon => alpha + carbon just barely touching each other What is the minimum initial kinetic energy of the alpha particle? Uf = K α + Kc Which term contains the unknown?