Answer: Same magnitude total momentum in both situations.

Transcription

1 Page 1 of 9 CTP-1. In which situation is the agnitude of the total oentu the largest? A) Situation I has larger total oentu B) Situation II C) Sae agnitude total oentu in both situations. I: v 2 (rest) II: v v 2 Answer: Sae agnitude total oentu in both situations. CTP-2. A car is sitting on the surface of the Earth and both the car and the Earth are at rest. (Pretend the Earth is not rotating or revolving around the Sun.) The car accelerates to a final velocity. After the car reaches its final velocity, the agnitude of the Earth's oentu is the agnitude of the car's oentu. A) ore than B) the sae as C) less than D) Cannot answer the question because the answer depends on the interaction between the Earth and the car. Answer: the sae as

2 Page 2 of 9 CTP-3. Suppose the entire population of Earth gathers in one location and, at a prearranged signal, everyone jups up. About a second later, 6 billion people land back on the ground. After the people have landed, the Earth's oentu is.. A) the sae as it was before the people juped. B) different than it was before the people juped. C) ipossible to know whether the Earth's oentu changed. Answer: the sae as it was before the people juped. After the 6 billion people have passed the apex of their jup and are on the way down, the velocity of the Earth is.. A) away fro the people B) toward the people C) zero Answer: toward the people The total oentu ust reain zero. It is the force of gravity on the Earth fro the people which is causing the Earth to ove toward the people. CTP-4. Two asses 1 and 2 are approaching each other on a frictionless table and collide. Is it possible that, as a result of the collision, all of the kinetic energy of both asses is converted to heat? A) Yes, all KE can disappear B) No, ipossible Answer: Yes, all KE can disappear. If the total oentu is zero, everything can stop after the collision, with the KE copletely converted into theral energy. A oving ass 1 is approaching a stationary ass 2 on frictionless table. Is it possible that, as a result of the collision, all of the kinetic energy of both asses is converted to heat? A) Yes B) No Answer: No. Since total oentu before the collision is non-zero, the total oentu after the collision ust be non-zero.

3 Page 3 of 9 CTP-5. Two asses, of size and 3, are at rest on a frictionless surface. A copressed, assless spring between the asses is suddenly allowed to uncopress, pushing the asses apart. 3 After the asses are apart, the speed of is the speed of 3. A) the sae as B) twice C) three ties D) 4 ties E) none of these The kinetic energy of is the kinetic energy of 3. (Hint: If P tot = 0, then A v A = B v B.) A) the sae as B) greater than C) less than While the spring is in contact with both asses, the agnitude of the acceleration of 3 is that of. A) the sae as B) greater than C) less than Answers: 1) three ties 2) greater than 3) less than

4 Page 4 of 9 CTP-6. A ball bounces off the floor elastically as shown. The direction of the ipulse of the ball, p, is... A) straight up B) straight down C) to the right D) to the left Answer: straight up CTP-7. Consider two carts, of asses and 2, at rest on an air track. If you push first one cart for 3 s, and then the other for the sae length of tie, exerting equal force on each, the oentu of the light cart is the oentu of the heavy cart. A) four ties B) twice C) equal to D) one-half E) one-quarter F for tie t F for tie t 3 Answer: equal to Use p = F net t

5 Page 5 of 9 CTP-8. Suppose a tennis ball and a bowling ball are rolling toward you. Both have the sae oentu, and you exert the sae force to stop each. How do the tie intervals to stop the copare? A) It takes less tie to stop the tennis ball. B) Both take the sae tie. C) It takes ore tie to stop the tennis ball. Answer: Both take the sae tie. CTP-9. A fast-ball thrown at a batter has a oentu of agnitude p i = (0.3kg)(40/s) = 12 kg /s. The batter hits the ball in a line drive straight back at the pitcher with oentu of agnitude p f = (0.3kg)(80/s) = 24 kg /s. What is the agnitude of the ipulse p? A) p f p i = 12 kg /s B) p f + p i = 36 kg /s C) p f = 24 kg /s D) None of these Answer: p f + p i = 36 kg /s Draw a p1/p2/ p diagra. CTP-10. A big ball, ass M=10, speed v, strikes a sall ball, ass, at rest. Could the following occur?: The big ball coes to a coplete stop and the sall ball takes off with speed 10v. (Assue that both balls reain at the sae teperature.) 10 v M 10v A) Yes, this can occur. B) No, it cannot occur because it would violate oentu conservation C) No, it cannot occur because it would violate energy conservation Answer: It cannot occur because it would violate energy conservation. The total KE of the syste after the collision is 10 ties the KE before the collision. Since the teperatures don t change, we need not worry about theral energy. Although you can convert KE into E_theral with 100% efficiency, you can't go the other way. You cannot convert E_theral into KE with 100% efficiency.

6 Page 6 of 9 CTP-11. Ball 1 strikes stationary Ball 2 in 1D elastic collision. The initial oentu of Ball 1, p 1 i, and the final oentu of Ball 2, p 2 f, are shown on the graph. In units shown on the graph, what is p 1 f? (To the right is positive.) A) 0 B) +1 C) 2 D) 1 E) Answer depends on whether collision was elastic or not 1 2 p 1i p 2f Answer: p 1f = 1 Since p tot = +3

7 Page 7 of 9 CTP-12. Ball 1 strikes stationary Ball 2 in 2D collision. The initial oentu of Ball 1, p 1 i, and the final oentu of Ball 2, p 2 f, are shown on the graph. What is the x-coponent of p 1 f (in units shown on graph)? A: 0 B: 1 C: 2 D: 3 E: None of these 1 2 p 2f p 1i Answer: p 1f, x = +1 Incidentally p 2f = 2

8 Page 8 of 9 CTP-13. A projectile is fired with initial speed v o at an angle of 45 o above the horizontal. Assue no air resistance. True A or False B: During the flight, the x-coponent of the projectile's oentu reains constant. True A or False B: During the flight, the y-coponent of the projectile's oentu reains constant. Answer: The x-coponent oentu reains constant because there no external force in the x-direction. For otion in the x-direction, the syste is isolated. The y-coponent of the oentu does not reain constant, because there is an external force (gravity) in the y-direction. For otion in the y-direction, the syste is not isolated. CTP-14. A bullet of ass and velocity v is fired into a wood block of ass M initially at rest on a frictionless surface. The bullet buries itself in the wood block and then the wood block is seen to have a final velocity v f. v M no friction M v f Before After Was this an elastic collision? A) Yes B) No True (A) or False (B): v =Mv f True (A) or False (B): (1/2)v 2 = (1/2)(M+) v f 2 Answers: 1) This is not an elastic collision. A lot of heat was generated as the bullet slid into the wood block. 2) False. Conservation of oentu iplies v =(M+)v f 3) False. Since this was an inelastic collision, soe of the KE was converted into E theral. KE is not conserved in this collision.

9 Page 9 of 9 CTP-15. Four floor tiles are laid out in an L-pattern as shown. The origin of the x-y axes is at the center of the lower left tile. y a x What is the x-coordinate of the center of ass? A: a B: (1/2)a C: (1/3)a D: (1/4)a E: none of these What is the y-coordinate of the center of ass? A: a B: 2a C: (3/4)a D: (5/4)a E: none of these Answers: Xc = (1/4)a Yc = (3/4)a