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1. Which of the following statements are true about momentum?
Answer: ADGHK a. TRUE  Momentum is a vector quantity. Like all vector quantities, the momentum of an object is not fully described until the direction of the momentum is identified. Momentum, like other vector quantities, is subject to the rules of vector operations. b. FALSE  The Joule is the unit of work and energy. The kg m/s is the standard unit of momentum. c. FALSE  An object has momentum if it is moving. Having mass gives an object inertia. When that inertia is in motion, the object has momentum. d. TRUE  This is true. However, one should be quick to note that the object does not have to have a constant speed in order to have momentum. e. FALSE  The direction of an object's momentum vector is in the direction that the object is moving. If an object is traveling eastward, then it has an eastward momentum. If the object is slowing down, its momentum is still eastward. Only its acceleration would be westward. f. FALSE  To say that momentum is a conserved quantity is to say that if a system of objects can be considered to be isolated from the impact of net external forces, then the total momentum of that system is conserved. In the absence of external forces, the total momentum of a system is not altered by a collision. However, the momentum of an individual object is altered as momentum is transferred between colliding objects. g. TRUE  Momentum is calculated as the product of mass and velocity. As the speed of an object increases, so does its velocity. As a result, an increasing speed leads to an increasing momentum  a direct relationship. h. TRUE  For the same speed (and thus velocity), a more massive object has a greater product of mass and velocity; it therefore has more momentum. i. FALSE  A less massive object would have a greater momentum owing to a velocity which is greater than that of the more massive object. Momentum depends upon two quantities * mass and velocity. Both are equally important. j. FALSE  When comparing the size of two momentum vectors, the direction is insignificant. The direction of any vector would never enter into a size comparison. k. TRUE  Objects with a changing speed also have a changing velocity. As such, an object with a changing speed also has a changing momentum. 
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2. Which of the following are true about the relationship between momentum end energy?
Answer: BE a. FALSE  No. Momentum is momentum and energy is energy. Momentum is NOT a form of energy; it is simply a quantity which proves to be useful in the analysis of situations involving forces and impulses. b. TRUE  If an object has momentum, then it is moving. If it is moving, then it has kinetic energy. And if an object has kinetic energy, then it definitely has mechanical energy. c. FALSE  If an object does NOT have momentum, then it definitely does NOT have kinetic energy. However, it could have some potential energy and thus have mechanical energy. d. FALSE  Consider Object A with a mass of 10 kg and a velocity of 3 m/s. And consider Object B with a mass of 2 kg and a velocity of 10 m/s. Object A clearly has more momentum. However, Object B has the greatest kinetic energy. The kinetic energy of A is 45 J and the kinetic energy of B is 100 J. e. TRUE  When comparing the momentum of two objects to each other, one must consider both mass and velocity; both are of equal importance when determining the momentum value of an object. When comparing the kinetic energy of two objects, the velocity of an object is of double importance. So if two objects of different mass have the same momentum, then the object with the least mass has a greater velocity. This greater velocity will tip the scales in favor of the least massive object when a kinetic energy comparison is made. 
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3. Which of the following statements are true about impulse?
Answer: BDFGHI a. FALSE  Impulse is NOT a force. Impulse is a quantity which depends upon both force and time to change the momentum of an object. Impulse is a force acting over time. b. TRUE  Impulse is a vector quantity Like momentum, impulse is not fully described unless a direction is associated with it. c. FALSE  An object which is traveling east could encounter a collision from the side, from behind (by a fastermoving object) or from the front. The direction of the impulse is dependent upon the direction of the force exerted upon the object. In each of these scenarios, the direction of the force would be different. d. TRUE  In a collision, there is a collision force which endures for some amount of time. The combination of force and time is what is referred to as an impulse. e. FALSE  The Newton is the unit of force. The standard metric unit of impulse is the N•s. f. TRUE  The N•s is the unit of momentum. The Newton can be written as a kg•m/s^2. When substituted into the N•s expression, the result is the kg m/s. g. TRUE  In a collision, there is a collision force which endures for some amount of time to cause an impulse. This impulse acts upon the object to change its velocity and thus its momentum. h. TRUE  Yes!!! This is the impulsemomentum change theorem. The impulse encountered by an object in a collision causes and is equal to the momentum change experienced by that object. i. TRUE  A force of 100 N for 0.10 s results in an impulse of 10 N•s. This 10 N•s impulse is equivalent to the impulse created by a force of 5 N for 2.0 seconds. 
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4. Which of the following statements are true about collisions?
Answer: ABF a. TRUE  In any collision between two objects, the colliding objects exert equal and opposite force upon each other. This is simply Newton's law of actionreaction. b. TRUE  In a collision, there is a collision force which endures for some amount of time to cause an impulse. This impulse acts upon the object to change its momentum. c. FALSE  The impulse encountered by an object is equal to mass multiplied by velocity change  that is, momentum change. d. FALSE  Two colliding objects will only experience the same velocity change if they have the same mass and the collision occurs in an isolated system. However, their momentum changes will be equal if the system is isolated from external forces. e. FALSE  This statement is mistaking the term velocity for momentum. It is momentum which is conserved by an isolated system of two or more objects. f. TRUE  Two colliding objects will exert equal forces upon each other. If the objects have different masses, then these equal forces will produce different accelerations. g. FALSE  It the colliding objects have different masses, the equal force which they exert upon each other will lead to different acceleration values for the two objects. h. FALSE  Total momentum is conserved only if the collision can be considered isolated from the influence of net external forces. i. FALSE  In any collision, the colliding objects exert equal and opposite forces upon each other as the result of the collision interaction. There are no exceptions to this rule. j. FALSE  In any collision, the colliding objects will experience equal (and opposite) momentum changes, provided that the collision occurs in an isolated system. k. FALSE  In any collision, the colliding objects exert equal and opposite forces upon each other as the result of the collision interaction. There are no exceptions to this rule. l. FALSE  In any collision, the colliding objects will experience equal (and opposite) momentum changes, provided that the collision occurs in an isolated system. 
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5. Which of the following statements are true about elastic and inelastic collisions?
Answer: AEFGI a. TRUE  A perfectly elastic collision is a collision in which the total kinetic energy of the system of colliding objects is conserved. Such collisions are typically characterized by bouncing or repelling from a distance. In a perfectly inelastic collision (as it is sometimes called), the two colliding objects stick together and move as a single unit after the collision. Such collisions are characterized by large losses in the kinetic energy of the system. b. FALSE  Few collisions are completely elastic. A completely elastic collision occurs only when the collision force is a noncontact force. Most collisions are either perfectly inelastic or partially inelastic. c. FALSE  Momentum can be conserved in both elastic and inelastic collisions provided that the system of colliding objects is isolated from the influence of net external forces. It is kinetic energy that is conserved in a perfectly elastic collision. d. FALSE  In a perfectly elastic collision, in an individual object may gain or lose kinetic energy. It is the system of colliding objects which conserves kinetic energy. e. TRUE  Kinetic energy is lost from a system of colliding objects because the collision transforms kinetic energy into other forms of energy  sound, heat and light energy. When the colliding objects don't really collide in the usual sense (that is when the collision force is a noncontact force), the system of colliding objects does not lose its kinetic energy. Sound is only produced when atoms of one object make contact with atoms of another object. And objects only warm up (converting mechanical energy into thermal energy) when their surfaces meet and atoms at those surfaces are set into vibrational motion or some kind of motion. f. TRUE  See above statement. g. TRUE  If large amounts of kinetic energy are conserved when a ball collides with the ground, then the postcollision velocity is high compared to the precollision velocity. The ball will thus rise to a height which is nearer to its initial height. h. FALSE  This is a perfectly elastic collision. Before the collision, all the kinetic energy is in the first glider. After the collision, the first glider has no kinetic energy; yet the second glider has the same mass and velocity as the first glider. As such, the second glider has the kinetic energy which the first glider once had. i. TRUE  There is significant bounce in the collision between a tennis racket and tennis ball. There is typically little bounce in the collision between a halfback and a linebacker (though there are certainly exceptions to this one). Thus, the ballracket collision tends to be more elastic. 
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Last update: 5/6/02