PHSC TEST 2
Here are the force diagrams for two carts being pushed forward as they move along separate tracks 1) >>>>>>>>>> force exerted on cart by hand>>>> CART 2) >>>> force exerted on cart by hand>>>>>>>>>> CART which of these two carts is moving faster? (notice the different sizes in arrows) A) Cart 1 B) Cart 2 C) Both are moving at the same speed D) it is impossible to tell
A)
The question again refers to the demonstration you previously saw that was referred to in the last question. assuming the speed of the cart is indeed constant, which one of these force diagrams is the most appropriate for the cart just after the initial push? A) >>>>> force exerted on force exerted cart by fan #1 on cart by fan #2 >>>>>>>>>>>>>>>>>CART<<<<<<<<<<<<<<< B) >>>>> >>>>>>>>>>>>>>>>>CART<<<<<<<<<<<<<<< >>>>> top arrows=force top arrows= exerted on cart by fan 1 force bottom= force exerted exerted on on cart by hand cart by fan 2 C) >>>>>>>>>>>>>>>>>CART<<<<<<<<<<<<<<< force exerted on force exerted on cart by fan #1 cart by fan #2
A)
if no sideways forces act on a moving object, what will its path be like? a) it will move in a zigzag pattern b) it will move in a straight line c) it will move in a circular path
B)
A child's sled is sliding across a frozen lake toward a patch of thin ice. To try and prevent this, you lasso the sled and pull the rope in the opposite direction to its motion to try and slow it down. Which of the diagrams below would best represent the situation, assuming it is for a moment in time before you successfully brought the sled to a stop? >>>>>> A) CART>>>>>>>force exerted on sled by rope <<<<<< B)CART<<<<<<<<force exerted on sled by rope <<<<<< C)CART>>>>>>>>force exerted on sled by rope
C)
Imagine tying a stuffed toy to a string and swinging it around in a horizontal circle above your head at a constant speed. the picture shows a top view at a particular moment in time, with the curve arrow simply indicating the direction of rotation. four dashed arrows (labeled A, B, C, D) point away from the toy at this position. which of these would be most appropriate to show the direction of the force acting on the toy at this particular moment in time? A) arrow a (pointing downward right) B) arrow b (pointing upward right) C) arrow c (upward) D) arrow d (downward left)
D)
several children of different ages and sizes are playing a tug-of-war game over a large box of toys. The force diagrams below indicate the forces that between one and four children are exerting on the box at different times. The friction force that the floor exerts on the box is also shown. In each case, the box is moving to the right (as indicated by the red speed arrow RSA) in which example is the speed of the box not constant? A) RSA >>>>>>> 175 N>>>>>>>>box<<<<< 125 N B) RSA>>>>>>> 225 N>>>>>>>>>>>>box<<<< 100 N <<< 75 n <<50 N (friction) C) RSA >>>>>>> 200 N>>>>>>>>>>>BOX<<<< 60 N << 40 N << 40 n <<< 50 N (friction) D) RSA>>>>>>>>> 50 N>>>> box <<<< 50 n (FRICTION)
c)
suppose you are watching an ice-hockey game with some classmates. As the puck is sliding across the ice at a relatively constant speed, it passes close to a player, who hits it (with his stick) in the same direction as it is already moving. After the hit, you notice that the puck is moving much faster after the hit than before. whose reasoning do you agree with? student A: "the force of the stick was transferred to the puck during the hit. After the hit, the puck has more force, so it moves faster." student B: "the puck still has the force that started it moving, which is what keeps it moving at a constant speed. When the player hit sit, he adds to this force, which makes the speed of the puck increase. After the hit, this extra force is gone, so the puck stops increasing in speed, but the original force is still there so now it moves at a faster constant speed." student C: "while the stick is in contact, it applies a force to the puck that makes its speed increase. as soon is contact is lost, this force disappears, so the speed of the puck stops increasing."
c) student C
Shown below are force diagrams for three carts that have different masses and are being pushed forward by different strength fans. If these three carts were in a race, which one would speed up at the slowest rate and hence lose the race? Select the cart that you think will finish last in a race between them. A) Force exerted on cart by fan 3.0 N >>>>>>>1.2 kg cart B) Force exerted on cart by fan 5.0 N >>>>>>1.8 kg cart C) Force exerted on cart by fan 2.0 N >>>>>>0.9 kg cart
C)
Two skateboarders start themselves moving at the same speed side-by-side. After their initial pushes, they slow down gradually due to the frictional force acting on each of them. The masses of the skateboarders and the strengths of the frictional forces are shown in the force diagrams below. >>>> >>>> person <<< 11 N person <<< 10 N 55 kg 45 kg Assuming they are initially moving at the same speed, which of the skateboard will slow to a stop first, and why? (HINT: think carefully about whether the first one to stop will have a higher or lower rate of change in his speed.) A) Skateboarder 2 will stop first because the quantity force strength/mass is higher for him. B) Skateboarder 1 will stop first because he has more mass. C) Skateboarder 1 will stop first because the quantity force strength/mass is lower for him. D) Skateboarder 1 will stop first because there is a stronger force acting opposite his motion.
A)
previously, you saw a demonstration (or a movie of one) involving a cart that had two fan units pushing on it in opposite directions with equal strength. with the cart initially at rest, it was given a push to start it moving. here is the force diagram for that cart when it is at rest. force exerted on force exerted on cart by fan #1 cart by fan #2 >>>>>>>>>>>>>>>>CART<<<<<<<<<<<<<< which one of these force diagrams is the most appropriate for the cart at a moment during the short period it is getting the push that starts it moving? A) force exerted on >>>> Force exerted cart by fan #1 on cart by fan #2 >>>>>>>>>CART<<<<<<<<<< force exerted >>>> on cart by hand B) force exerted on >>>>> force exerted cart by fan #1 on cart by Fan #2 >>>>>>>>>>>CART<<<<< C) same thing^^ but arrows are equal on both sides instead of unequal
A)
if the bumps on the sandpaper were very small compared to the barriers created by the sticky notes, what do you think is the most likely reason that the frictional force produced by the sandpaper stopped the block more quickly than the sticky notes? A) there was about the same number of backwards taps in each case, but each bump in the sandpaper produced a slightly stronger backwards tap than each sticky note. B) there were fewer bumps in the sandpaper than there were sticky notes, but each bump produced a much stronger backwards tap than each sticky note. C) The backward tap produced by each bump in the sandpaper was weaker than that produced by each sticky note, but the number of bumps in the sandpaper was much higher than the number of sticky notes that were used.
C)
in a question earlier in this extension, you considered the situation of moving a couch at a constant speed. you concluded that to move the couch at a constant speed, you would need to push it with a force that exactly balances the frictional force of 50 N acting on the couch. now consider a situation in which the couch is at rest. you push on the couch with a force of 25 N- and the couch still does not move. which one of the force diagrams below best describes this situation? A) force exerted on couch by you 25 N>>>>> COUCH B) force exerted on couch by you 25 N>>>>>COUCH<<<<<<<<<<<<<50 N frictional force exert on couch by floor C) force exerted on couch by you 25 N>>>>>>COUCH<<<<<<25 N frictional force exert on couch by floor
C)
now, suppose, after the toy has moved a bit further round the circle, the string were to break when the toy was in the position shown in the diagram. which of the dashed arrows best indicates the path the toy would follow after the string breaks? A) Path A (downward left) B) Path B (downward right) C) Path C (downward right... more right than B) D) Path D (upward right)
C)
when a 'sideways' force acts on a moving object, what effect does it have? A) it makes the object's speed increase B) it makes the object's speed decrease C) it changes the direction that the object is moving D) it has no effect on the object's motion
C)
while arguing over who owns a toy, two children, cindy and scott, both grab it and engage in a tug-of-war over it. at one certain moment in time during their struggle, the force diagram for thetoy looks like this: <<<<<<< <<<<<< teddy bear >>>>>>>> force exerted on toy by cindy force exerted on toy by scott which of the following statements best describes what this force diagram represents? a) scott is pulling harder than cindy, and the toy is moving toward him in this particular moment in time b) cindy is pulling harder than scott, and the toy is moving toward her at this particular moment in time c) cindy is not pulling as hard as scott, but the toy is moving toward her at this particular moment in time d) at this particular moment in time scott and cindy are pulling equally hard, so the toy is not moving
C)
shown here is a force diagram for the skateboarder in this assignment at a time of 6 seconds after the simulator started (halfway through the period during which he was being pushed). >>>>> >>>>> person which of the force diagrams below would be most appropriate for him at a time of 10 seconds (well after the push has ended)? >>>>>>>>> a) person >>>>>>>>> b) >>>> person >>>>>>>>> c) >>>>>>>>person
A)
In unit EM, you saw how contact push/pull interactions can be described using ideas about energy transfers and changes. In this unit, you are developing ideas about how these same interactions can be described in terms of the forces acting on an object. Below is a list of ideas about how the energy and force descriptions of contact push/pull interactions might be related. Which of these are consistent with the evidence you have seen so far? (select all that apply) A) when a single force acts on a moving object in the same direction as its motion, its KE increases. B) when a dingle force acts on a moving object in the same direction as its motion, energy is transferred out of the object to another object. C) when a single force acts on a moving object in the same direction as its motion, the object is an energy receiver in a contact push/pull interaction. D) if the KE of a moving object is staying constant, a force must be pushing it forward, even if the effects of friction can be ignored.
A) & C)
In many situations studied in physics, the effect of the drag force is ignored. Such situations would include the carts moving along the tracks that you have seen presented in class. why can the drag force be neglected in such situations? A) the experiments were done in a vacuum, so no air was present. B) the speeds of the carts were low enough that the drag forces action on them were very weak. C) The carts are small enough that there would be no drag force acting on them, no matter how fast they were moving.
B)
Shown here is a force diagram for the skateboarder in this assignment at a time of 6 seconds after the stimulator started (halfway through the period during which he was being pushed). The first two questions of the quiz concern appropriate force diagrams for him at two other times. >>>>>>>>> >>>>> PERSON Which of the force diagrams below would be most appropriate for him at a time of 2 seconds (well before the push started)? >>>> A). >>>>> person >>>> B) person >>>>>>>> C) person
B)
When shopping for a new car, a professor was surprised to learn that a certain small compact car (mass=800 kg) will speed up (accelerate) at a faster rate than a large SUV (mass=2200 kg), although the SUV has the more powerful engine. What is the reason that the compact car can speed up at a faster rate than the SUV, despite having a less powerful engine? A) The quantity pushing force * mass is smaller for the compact car. B) The quantity pushing force / mass is greater for the compact car. C) The quantity pushing force / mass is smaller for the compact car. D) The quantity pushing force * mass is greater for the compact car.
B)
You have been using an analogy between a row of sticky notes and the sandpaper surface to develop your ideas about how a frictional force is produced when a block slides across sandpaper. However, you have seen that even when the block slides across an apparently smooth tabletop, it still slows down. Consider how our analogy might be extended to explain how a frictional force is produced when the block slides across and apparently smooth surface. what do you think you would see if you looked at a smooth tabletop with a powerful magnifier? A) a thin layer of moisture on the surface that makes it somewhat 'sticky' B) very small bumps and grooves in the surface C) nothing. it would still look perfectly smooth
B)
frank and hector are moving two boxes across a rough floor. Frank pushes a 20 kg box with a force of 85 N while a frictional force of 75 N acts on it in the opposite direction. Meanwhile, hector pushes on the 30 kg box with a force of 105 N while a frictional force of unknown strength acts on it. 1) Force exerted on Force exerted on 20 kg box by Frank 20 kg box by >>> floor >>>>>>>>>> 20 kg <<<<<<< 85 N 75 N 2) Force exerted on frictional force 30 kg box by hector exerted on 30kg box by floor >>> >>>>>>> 30 kg <<<<<<< 105 N ?? N A) 75 N B) 90 N C) 93 N D) 95 N
B)
shown to the right are the speed-time and force-time graphs from a simulator. which of these statements is consistent with what the graphs show is happening to the simulator cart at t=9 seconds? *one graph shows a line increase, then straight/horizontal, then increase, the horizontal. at 9, it is straight and horizontal. the second graph has three bars, not connected, and at 9 theres not bar to observe. however the flat line at top of it is at 9* A) its Kinetic energy is increasing and no force is acting on it. B)its Kinetic energy is constant and no force is acting on it. C)its Kinetic energy is increasing and a force is acting on it. D)its Kinetic energy is decreasing and a force is acting on it.
B)
some students were comparing their ideas about how friction works with a demonstration they saw in an earlier lesson, in which several very gentle 'backward' taps were applied to a moving cart, thereby slowing down in several 'steps'. One student made the following statement: "when we slowed the cart down in the lesson 4, we were applying several weak 'backward' forces to it. Each one of these forces made the cart slow down a little, until eventually it stopped. But friction is different, there are no backward forces acting on the block, it's just the rubbing on the surface that makes it slow down." A) I agree with this student. the two processes are very different from each other. B) i disagree with this student. There are backward forces action on an object when it slides across a surface that are very like the backwards taps applied to a cart by someone's hand.
B)
At the start of this extension, you considered a conversation between two students: Dave- "I think energy and force are both the same. During a contact push/pull interaction both energy and force are transferred from one object to another. so, after the interaction one object has more energy and force than it had before, and the other has less energy and force." Luisa- "I dont think they are the same. I think that the force is only there while the two objects interact with each other and thats when the energy is transferred. when there is no interaction, there is no force, and so no transfer of energy." which student's thinking is consistent with both the energy-based and force-based models of contact push/pull interactions? A)dave B)luisa C)both D)neither
B) Luisa
a moving cart is given a push by someones hand so that a force is exerted on it. The force diagram for a moment in time while this force is acting is shown here. >>>>>>>>>>> >>>>>>(force exerted on cart by hand)>>>CART several seconds later it is observed that the cart is still moving, but measurements show that the force of the hand is no longer acting on the cart. Which of the force diagrams below would be most appropriate for the cart at this later moment in time? >>>>>>> A) >>>>> force exerted on cart by hand> CART B)>>>>>>> force exerted on cart by hand>> CART >>>>>>> C)CART
C)
after a hockey player gives a puck a quick hit with his stick, the puck slides across the ice at a speed that is essentially constant. a student in a previous class offered the following force diagram and explanation for why the speed of the puck is constant after the hit. "the initial hit exerts a force on the puck, making the forces acting on the puck unbalanced, and so it starts to move. After the hit ends there is no net force acting on the puck, and when the nete force acting on an object is zero, its speed does not change. so after the stick has lost contact with the puck, its speed remains constant." what is your evaluation of this explanation? A) Both the force diagram and the narrative are accurate B) The force diagram is accurate but the narrative is problematic. C) The force diagram is problematic but the narrative is accurate. D) Both the force diagram and the narrative are problematic.
C)
after completing the first part of this hw assignment, luisa made this comment: "I dont understand how an object with balanced forces acting on it can be moving at all. after all, didnt we learn that an object at rest, with balanced forces acting on it, will stay at rest?" which of the following statements best addresses Luisa's concern? A) Another push is needed to start such an object moving, but during that push, the forces are still balanced B) Luisa is correct. An object with balanced forces cannot be moving. C) Another push is needed to start such an object moving, and during that push, the forces are unbalanced.
C)
Consider the force diagrams for sour low-friction carts shown below. Each cart is subject to pushes from two fans (not shown) mounted on opposite ends of the cart. The forces the fans exert of the carts are shown. all four carts are moving to the right (the speed arrows are not shown). In each case, the cart experiences a small friction force in the opposite direction to its motion. these friction forces are also shown. each cart has a mass of 1 kg, but three of the carts also carry objects that contribute to their total mass. the total mass of each cart and the object it carries (if any) is indicated in the force diagrams below. which cart experiences the greatest rate of change in speed? A) 50 N>>>>>CART<<<<<35 n 4 KG <<< 15 n (friction) B). 20 N>>>cart<<<<< 35 N 2.4 kg. << 9 n (friction) C) 50 N>>>>>CART <<<<<40 N 1 KG << 4 N (friction) D) 100 N>>>>>>>>>>>cart<<<<< 40 N 3.2 kg 12 N (friction)
D)
here is a force diagram for a cart at a particular moment in time. >> force exerted on cart by hand>>>>>>Cart assuming the same force continues to act, how will this cart's kinetic energy in a few seconds compare with its kinetic energy now, and why? A) its KE will be the same because the force stays the same. B)it will have less KE because the force will slow it down. C) its KE will be the same because no energy is being transferred to it. D) it will have more KE because energy is being transferred to it.
D)
at the beginning of this extension activity, we asked how we could tell which of the two boxes below would speed up at the higher rate. The ideas you have developed in this assignment should help you decide the answer to this question. 1) 300 N 500 N >>>> 50 kg CART <<<<<<<<<<<<< >>>>>>> 400 N 2) 150 N >>>>>>>>>>>> 35 kg CART <<<< 500 N <<<<<<<<<< 200 N which of these two boxes will speed up at a higher rate, and why? A) the 50 kg box will speed up at a higher rate because the net force acting on it is stronger. B) The 35 kg box will speed up at a higher rate because it has less mass. C) The 50 kg box will speed up at a higher rate because the quantity net force strength/mass is greater for this box. D) The 35 kg box will speed up at a higher rate because the quantity net force strength/mass is greater for this box.
d)