CHAPTER 7 TEST REVIEW -- MARKSCHEME

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1 AP PHYSICS Nae: Period: Date: Points: 53 Score: IB Curve: DEVIL PHYSICS BADDEST CLASS ON CAMPUS 50 Multiple Choice 45 Single Response 5 Multi-Response Free Response 3 Short Free Response 2 Long Free Response AP EXAM CHAPTER TEST 90 in, 1 point each 25 Multiple Choice 45 in 22 Single Response 3 Multi-Response 90 in Free Response 13 in ea, 7 pts ea 2 Short Free Response 25 in ea, 12 pts ea 1 Long Free Response 45 in 12 in ea, 7 pts ea 20 in ea, 12 pts ea MULTIPLE CHOICE CHAPTER 7 TEST REVIEW -- MARKSCHEME 1. A rubber ball and a lup of putty have equal ass. They are thrown with equal speed against a wall. The ball bounces back with nearly the sae speed with which it hit. The putty sticks to the wall. Which object experiences the greater oentu change? a. The ball b. The putty c. The wall d. All experience the sae oentu change e. Cannot be deterined fro the inforation given 2. If you pitch a baseball with twice the kinetic energy you gave it in the previous pitch, the agnitude of its oentu is Since ass doesn t change, only the velocity changes a. The sae b ties as uch so, c. 2 ties as uch d. 4 ties as uch e. Cannot be deterined without knowing the ass of the baseball 3. Two equal ass balls (one red and the other blue) are dropped fro the sae height, and rebound off the floor. The red ball rebounds to a higher position. Which ball is subjected to the greater agnitude of ipulse during the collision with the floor? a. It s ipossible to tell since the tie intervals and forces are unknown b. Both balls were subjected to the sae agnitude ipulse c. The blue ball d. The red ball e. The floor Reeber that the rebound velocity is in the opposite direction so it is negative If the red ball rebounded higher, ore of its kinetic energy was conserved, which eans higher velocity which eans ore oentu Chapter 7 Test Review Markschee Updated: 22-Mar-15 Page 1 of 11

2 4. A 100 kg football linebacker oving at 2.0 /s tackles head-on an 80 kg halfback running 3.0 /s. Neglecting the effects due to digging in of cleats a. The linebacker will drive the halfback backward b. The halfback will drive the linebacker backward Since the halfback has ore oentu, c. Neither player will drive the other backward the linebacker will be driven backward d. They will both ove backward the sae aount e. Cannot be deterined without knowing the teas they play for 5. A golf ball traveling 3.0 /s to the right collides in a head-on collision with a stationary bowling ball in a friction-free environent. If the collision is alost perfectly elastic, the speed of the golf ball iediately after the collision is a. Slightly less than 3.0 /s b. Slightly greater than 3.0 /s c. Equal to 3.0 /s d. Much less than 3.0 /s e. Cannot be deterined without knowing the ass of the two balls In an elastic collision, kinetic energy is conserved, BUT the golf ball will transfer a slight aount of its oentu to the bowling ball so its rebound velocity will be slightly less. 6. A kg tennis ball, initially oving at a speed of 12 /s, is struck by a racket causing it to rebound in the opposite direction at a speed of 18 /s. What is the change in oentu of the ball? a kg /s Reeber that the rebound velocity is in the opposite direction so it is negative b kg /s c kg /s d. 1.1 kg /s e. 1.8 kg /s 7. A 70-kg astronaut is space-walking outside the space capsule and is stationary when the tether line breaks. As a eans of returning to the capsule he throws his 2.0 kg space haer at a speed of 14 /s away fro the capsule. At what speed does the astronaut ove toward the capsule? a /s Moentu is conserved b. 1.5 /s c. 3.5 /s d. 5.0 /s e. 7.0 /s 8. A 1000 kg car traveling at 25 /s runs into the rear of a stopped car that has a ass of 1500 kg and they stick together. What is the speed of the cars after the collision? a. 5.0 /s Tooootally Inelastic Collision Moentu Conserved b. 10 /s c. 15 /s d. 20 /s e. 25 /s Chapter 7 Test Review Markschee Updated: 22-Mar-15 Page 2 of 11

3 9. A 0.10 kg ball is dropped onto a table top. The speeds of the ball right before and right after hitting the table top are 5.0 /s and 4.0 /s, respectively. If the collision between the ball and the table top lasts 0.15 s, what is the agnitude of the average force exerted on the ball by the table top? a N Ipulse b. 1.3 N c. 3.0 N d. 3.5 N e. 6.0 N 10. A fire hose is turned on the door of a burning building in order to knock the door down. This requires a force of 1000 N. If the hose delivers 40 kg per second, what is the iniu velocity of the strea of the strea needed, assuing the water doesn t bounce back? Ipulse a /s b. 15 /s c. 20 /s d. 25 /s e. 30 /s 11. ( /1) Which one of the following stateents concerning oentu is true? a. Moentu is a force it s not b. Moentu is a scalar quantity no, it s a vector c. The SI unit of oentu is the kilogra-eter squared per second or kg 2 /s no, it s kg /s d. The oentu of an object is always positive no, soeties it is negative e. Moentu has the sae units as ipulse 12. ( /1) A 0.1 kg steel ball is dropped straight down onto a hard, horizontal floor and bounces straight up. Its speed iediately before and iediately after ipact with the floor is 10.0 /s. What is the agnitude of the ipulse delivered to the floor by the steel ball? a. 0 N s Ipulse b. 1 N s c. 2 N s d. 10 N s e. 100 N s 13. ( /1) A bea of n gas olecules is incident upon a barrier at 30 relative to the horizontal as shown. Each olecule has ass and speed v, and the entire bea is reflected elastically, also at 30. What is the agnitude of the total change of oentu of the particle bea during this event? a. 2nv b. 1.73nv c nv d nv e. Nv The x-coponent of the oentu (v cos 30 ) is the sae for both so they cancel out. The y-coponents (v sin 30 ) are in opposite directions so they are additive. Also, you ust ultiply the oentu of each olecule by the nuber of olecules (n). Chapter 7 Test Review Markschee Updated: 22-Mar-15 Page 3 of 11

4 14. ( /1) Which of the following five objects requires the greatest change in oentu to stop it? Object Mass (kg) Speed (/s) Moentu (a) Electron (b) Oil Tanker (c) Raindrop (d) Snail (e) Satellite ( /1) A baseball of ass (at rest, T-ball?) is struck by a bat so that it acquires a speed v. If t represents the duration of the collision between the bat and the ball, which expression deterines the agnitude of the average force exerted on the ball? a. b. c. t d. Ipulse e. vt 16. ( /1) A sled of ass is coasting on a frozen river when, while passing under a bridge, a box of ass falls straight down and lands on the sled. The sled and box continue along the original line of otion. How does the kinetic energy of the sled with the box copare to the original kinetic energy of the sled? a. It is one-fourth the original kinetic energy of the sled Moentu is conserved b. It is one-half the original kinetic energy of the sled c. It is three-fourths the original kinetic energy of the sled d. It is the sae as the original kinetic energy of the sled e. It is two ties the original kinetic energy of the sled ( /1) A 2.0 kg object is acted upon by a single force in the positive x-direction as shown. What is the oentu change experienced by the object during the first 6 s? a N s b N s c N s d N s e N s 10.0 F(N) t(s) Ipulse Area under an F vs. t graph is equal to ipulse Chapter 7 Test Review Markschee Updated: 22-Mar-15 Page 4 of 11

5 17. ( /1) An in-flight projectile in dynaic equilibriu explodes into several fragents. What happens instantaneously to its oentu following this explosion? a. It has been changed into kinetic energy of the fragents b. It is less than that iediately before the explosion c. It is the sae as that iediately before the explosion, by the law of conservation of oentu d. It is ore than that iediately before the explosion. e. It has been changed into radiant energy v 2 = 2v v 3 Conservation of Moentu 1 2 v ( /1) A projectile has just exploded into three pieces, with the velocities of each piece as shown. What was the speed of the projectile the instant before it broke up? a. b. c. d. e. 19. A rifle of ass M is initially at rest but is free to recoil. It fires a bullet of ass and velocity +v (relative to the ground). After firing, what is the velocity of the rifle (relative to the ground)? a. b. c. d. e. Conservation of Moentu Chapter 7 Test Review Markschee Updated: 22-Mar-15 Page 5 of 11

6 For questions 21 and 22, refer to the following inforation: A space vehicle of ass has a speed v. At soe instant, it explodes into two pieces, each of ass ½. One of the pieces is at rest just after the separation. This event occurs very far fro any celestial body. 20. Which of the following stateents concerning this situation is true? a. The oving piece has speed 2v. Conservation of Moentu b. The oving piece has speed v. c. The piece at rest possesses kinetic energy. d. The oving piece has speed ½ v. e. This process does not conserve oentu. 21. What is the kinetic energy of the oving piece just after the separation? a. 0 Conservation of Moentu b. ¼ v 2 c. ½ v 2 d. v 2 e. 2 v A 50.0 kg boy runs at a speed of 10.0 /s and jups onto a cart that is initially at rest. If the speed of the cart with the boy on it is 2.50 /s, what is the ass of the cart? a kg Moentu is conserved b kg c kg d kg e kg 23. An object of oentu p and ass is in otion. At the oent it is oving with speed v, what is its kinetic energy? Definition of oentu and kinetic energy a. b. c. d. e. 24. Which of the following stateents concerning an inelastic collision is true? (circle all that apply) a. Total ass and oentu are conserved. b. Total ass is not conserved, but oentu is conserved. oentu is always conserved c. Neither kinetic energy nor oentu is conserved. oentu is always conserved d. Moentu is conserved, but kinetic energy is not conserved. e. The total ipulse is equal to the change in ass. ipulse = change in oentu f. The total ipulse is equal to the change in oentu. Chapter 7 Test Review Markschee Updated: 22-Mar-15 Page 6 of 11

7 FREE RESPONSE v = 10 /s 25. A 26.0 kg boy is standing at rest on a 4.0 kg skateboard at the botto of a frictionless, but uneven, hill as shown. A 5.0 kg ball coes at hi with a horizontal velocity of 10.0 /s to the right, and he catches the ball and reains on the skateboard. a. ( /2) Deterine the speed of the boy the oent after he catches the ball. b. ( /3) Deterine how high up the hill the boy with the ball on the skateboard coasts until oentarily (no pun intended) coing to rest. c. ( /2) Sketch the free-body diagra of the boy as he stops on the hill in the diagra below. F N d. ( /2) The boy now begins to accelerate down the hill, which is tilted relative to the horizontal by the angle θ. Derive an expression for the boy s acceleration in ters of g and θ θ F g F g =g F g-x =g sin(θ) Chapter 7 Test Review Markschee Updated: 22-Mar-15 Page 7 of 11

8 e. ( /1) What percentage of Earth s gravitational acceleration is the boy s acceleration if the angle of the hill is 49? 2 of fuel 2 of exhaust gas 26. A rocket of ass initially carries an additional ass of fuel equal to 4 as shown. The rocket is in deep space, very far fro any stars or planets, and therefore has negligible external forces on it and is initially at rest. The rocket engine fires, causing the rocket to consue (at a constant rate) a ass of 2 of fuel expelled out the nozzle as hot gas oving at speed v (relative to the original rest frae). Left behind is 2 of unburned fuel. a. ( /1) After the gas is eitted, what is the agnitude of the oentu of the exhaust gas? Express your answer in ters of and v. b. ( /2) After the gas is eitted, what is the speed of the rocket? Express your answer in ters of and v. c. ( /2) If the tie during which the gas is expelled is t, what was the average force F on the rocket by the gas during the fuel burn? Express your answer in ters of, v and t. Chapter 7 Test Review Markschee Updated: 22-Mar-15 Page 8 of 11

9 27. A ball of ass 400 g oving toward the east with a speed of 3.70 /s collides head-on with a 200 g ball sitting at rest. The collision is perfectly elastic. a. ( /3) Deterine the velocity (agnitude and direction) of the first ball after the collision. Define east as positive direction and west as negative direction east b. ( /2) Deterine the velocity (agnitude and direction) of the second ball after the collision. fro a. above east c. ( /2) Show that kinetic energy is conserved in this collision. 28. A 15 g bullet travelling 213 /s in a vertical direction buries itself in a 2.4 kg block of wood at rest directly above it. As a result, the bullet/block cobination oves vertically upward. a. ( /2) Deterine the velocity of the bullet/block cobination iediately after ipact. Reeber to convert the ass of the bullet fro gras to kilogras Chapter 7 Test Review Markschee Updated: 22-Mar-15 Page 9 of 11

10 b. ( /2) Deterine the axiu height reached by the bullet/block cobination Since the bullet and block stick together, it is an inelastic collision. This eans you can t use conservation of energy and you ust use a kineatic equation c. ( /3) Prove whether or not echanical energy is conserved. No, it is an inelastic collision. Prove it by coparing the kinetic energy of the bullet to either the kinetic energy of the cobination or the gain in potential energy of the cobination 4 The lost energy was taken up by the work due to friction between the bullet and the wood in stopping the bullet s otion. That work was used to create heat. Chapter 7 Test Review Markschee Updated: 22-Mar-15 Page 10 of 11

11 29.. a. ( /X) v 2 = 2v v v 1 v = 10 /s 2 of fuel 2 of exhaust gas Chapter 7 Test Review Markschee Updated: 22-Mar-15 Page 11 of 11