Honors Physics Conservation of Energy and Momentum Test
An object is moving to the right. A force acts leftward upon it. This force is doing negative work.
TRUE - A force which acts in a direction opposite the motion of an object will do negative work.
A kg•m2/s2 would be a unit of work.
TRUE - A kg•m2/s2 is a mass unit times a speed squared unit, making it a kinetic energy unit and equivalent to a Joule.
A force is exerted on an object to move it at a constant speed. The power delivered by this force is the magnitude of the force multiplied by the speed of the object.
TRUE - An equation for computing work in constant speed situations is P=F•v.
An object can never have a negative kinetic energy.
TRUE - Kinetic energy is determined by the equation 0.5•m•v2. the quantity m is always positive. And even if v is negative, v2 will always be positive. Therefore, kinetic energy can never be a negative value.
Power is a time-based quantity.
TRUE - Power is a rate quantity and thus time-based.
A 300-Newton force is applied to a skier to drag her up a ski hill at a constant speed of 1.5 m/s. The power delivered by the toe rope is 450 Watts.
TRUE - Since force and speed are given, use Power = F•v. The calculation yields 450 W.
A force is applied by a chain to a roller coaster car to carry it up the hill of the first drop of the Shockwave ride. This is an example of work being done.
TRUE - There is a component of force in the direction of displacement and so this is an example of work.
The force of friction acts upon a softball player as she makes a headfirst dive into third base. This is an example of work being done.
TRUE - There is a force and a displacement; the force acts in the opposite direction as the displacement and so this force does negative work.
Power refers to how fast work is done upon an object.
TRUE - This is the definition of power.
The standard metric unit of power is the Watt.
TRUE - Watt is the unit of power? Yes!!
A non-conservative force is doing work on an object; it is the only force doing work. Therefore, the object will either gain or lose mechanical energy.
TRUE - When non-conservative forces do work upon an object, the object will either gain or lose mechanical energy. Mechanical energy is conserved (neither gained nor lost) only when conservative forces do work upon objects.
Work is a form of energy.
TRUE - Work is a form of energy, and in fact it has units of energy.
kenetic energy formula
1/2mv^2
56. A cart with a mass of M is moving along a low-friction track with a speed of 60 cm/s. A brick is gently dropped from rest upon the cart. After the collision the cart and brick move together. ... If the brick has a mass of 2M, then the post-collision speed of the two objects will be _____________ cm/s. ... If the brick has a mass of 3M, then the post-collision speed of the two objects will be _____________ cm/s. ... If the brick has a mass of 4M, then the post-collision speed of the two objects will be _____________ cm/s. ... If the brick has a mass of 5M, then the post-collision speed of the two objects will be _____________ cm/s. ... If the brick has a mass of 0.5M, then the post-collision speed of the two objects will be _____________ cm/s. ... If the brick has a mass of 0.25M, then the post-collision speed of the two objects will be _____________ cm/s.
20 15 12 10 40 48
53. An object with a mass M and a velocity v has a momentum of 32 kg•m/s. An object with a mass of ... ... 2M and a velocity of 2v would have a momentum of _____________ kg•m/s. ... 2M and a velocity of 0.5v would have a momentum of _____________ kg•m/s. ... 0.5M and a velocity of 2v would have a momentum of _____________ kg•m/s. ... 0.5M and a velocity of 0.5v would have a momentum of _____________ kg•m/s. ... 4M and a velocity of v would have a momentum of _____________ kg•m/s. ... 4M and a velocity of 0.5v would have a momentum of _____________ kg•m/s. ... 0.5M and a velocity of 4v would have a momentum of _____________ kg•m/s. ... 3M and a velocity of 2v would have a momentum of _____________ kg•m/s
64 32 32 8 128 64 64 192
6. Which of the following objects have momentum? Include all that apply. a. An electron is orbiting the nucleus of an atom. b. A UPS truck is stopped in front of the school building. c. A Yugo (a compact car) is moving with a constant speed. d. A small flea walking with constant speed across Fido's back. e. The high school building rests in the middle of town.
A, C, and D Momentum can be thought of as mass in motion. An object has momentum if it has its mass in motion. It matters not whether the object is of large mass or small mass, moving with constant speed or accelerating; if the object is MOVING, then it has momentum!
27. A student applies a force to a cart to pull it up an inclined plane at a constant speed during a physics lab. A force of 20.8 N is applied parallel to the incline to lift a 3.00-kg loaded cart to a height of 0.450 m along an incline which is 0.636-m long. Determine the work done upon the cart and the subsequent potential energy change of the cart. PSYW
Answer: 13.2 J There are two methods of solving this problem. The first method involves using the equation W = F*d*cos(Theta) where F=20.8 N, d=0.636 m, and Theta=0 degrees. (The angle theta represents the angle betwee the force and the displacement vector; since the force is applied parallel to the incline, the angle is zero.) Substituting and solving yields W = F*d*cos(Theta) = (20.8 N)*(0.636 m)*cos(0) =13.2 J. The second method is to recognize that the work done in pulling the cart along the incline at constant speed changes the potential energy of the cart. The work done equals the potential energy change. Thus, W=Delta PE = m*g*(delta h) = (3.00 kg)*(9.8 m/s/s)*(0.45 m) =13.2 J
71. Two ice skaters collide on the ice. A 39.6-kg skater moving South at 6.21 m/s collides with a 52.1-kg skater moving East at 4.33 m/s. The two skaters entangle and move together across the ice. Determine the magnitude and direction of their post-collision velocity.
Answer: 3.64 m/s at 42.5 degrees east of south (312.5 degrees) explanation is too long, just go look at this link if you are confused https://www.physicsclassroom.com/reviews/Momentum-and-Collisions/Momentum-and-Collisions-Review-Answers-4
38. A baseball player catches a 163-gram baseball which is moving horizontally at a speed of 39.8 m/s. Determine the force which she must apply to the baseball if her mitt recoils a horizontal distance of 25.1 cm. PSYW
Answer: 514 N This is an example of work being done by a non-conservative force (the applied force of the mitt) upon a baseball in order to change its kinetic energy. So Wnc = Change in KE The change in kinetic energy can be computed by subtracting the initial value (0.5 • m • vi2) from the final value (0 J) . Change in KE = KEf - KEi = 0 J - 0.5 • (0.163 kg) • (39.8 m/s)2 = -129 J The force can be determined by setting this value equal to the work and using the expression for work into the equation: Wnc = -129 J F • d • cos(theta) = -129 J F • (0.251 m) • cos(180 deg) = -129 J F = 514 N
60. A 46-gram tennis ball is launched from a 1.35-kg homemade cannon. If the cannon recoils with a speed of 2.1 m/s, determine the muzzle speed of the tennis ball.
Answer: 62 m/s Given: mball = 46 g = 0.046 kg; mcannon = 1.35 kg; vcannon = -2.1 m/s Find: vball = ??? The ball is in the cannon and both objects are initially at rest. The total system momentum is initially 0. After the explosion, the total system momentum must also be 0. Thus, the cannon's backward momentum must be equal to the ball's forward momentum. mcannon• vcannon= -mball• vball (1.35 kg) • (-2.1 m/s) = (0.046 kg) • vball vball = (1.35 kg) • (2.1 m/s) / (0.046 kg) = 61.63 m/s = ~62 m/s
12. An arrow is drawn back so that 50 Joules of potential energy is stored in the stretched bow and string. When released, the arrow will have a kinetic energy of ____ Joules. a. 50 b. more than 50 c. less than 50
Answer: A A drawn arrow has 50 J of stored energy due to the stretch of the bow and string. When released, this energy is converted into kinetic energy such that the arrow will have 50 J of kinetic energy upon being fired. Of course, this assumes no energy is lost to air resistance, friction or any other non-conservative forces and that the arrow is shot horizontally.
16. A ball is projected into the air with 100 J of kinetic energy. The kinetic energy is transformed into gravitational potential energy on the path towards the peak of its trajectory. When the ball returns to its original height, its kinetic energy is ____ Joules. Do consider the effects of air resistance a. less than 100 b. 100 c. more than 100 d. not enough information given
Answer: A During any given motion, if non-conservative forces do work upon the object, then the total mechanical energy will be changed. If non-conservative forces do negative work (i.e., Fnc*d*cos(Theta) is a negative number), then the final TME is less than the initial TME. In this case, air resistance does negative work to remove energy from the system. Thus, when the ball returns to its original height, their is less TME than immediately after it was thrown. At this same starting height, the PE is the same as before. The reduction in TME is made up for by the fact that the kinetic energy has been reduced; the final KE is less than the initial KE.
13. A child lifts a box up from the floor. The child then carries the box with constant speed to the other side of the room and puts the box down. How much work does he do on the box while walking across the floor at constant speed? a. zero J b. more than zero J c. more information needed to determine
Answer: A For any given situation, the work done by a force can be calculated using the equation W = F*d*cos(Theta) where F is the force doing the work, d is the displacement of the object, and Theta is the angle between the force and the displacement. In this specific situation, the child is applying an upward force on the box (he is carrying it) and the displacement of the box is horizontal. The angle between the force (vertical) and the displacement (upward) vectors is 90 degrees. Since the cosine of 90-degrees is 0, the child does not do any work upon the box. A detailed discussion of a similar situation (the waiter and the tray of food) can be found at The Physics Classroom.
16. Suppose that you're driving down the highway and a moth crashes into the windshield of your car. Which undergoes the greater acceleration? a. the moth b. your car c. both the same
Answer: A In any collision, there are always four quantities which are the same for both objects involved in the collision. Each object experiences the same force (Newton's third law) for the same amount of time, leading to the same impulse, and subsequently the same momentum change. Only the acceleration and the velocity change can differ for the two objects. The object with the least mass always receives the greatest velocity change and acceleration.
18. A 10-Newton object moves to the left at 1 m/s. Its kinetic energy is approximately ____ Joules. a. 0.5 b. 1 c. 10 d. more than 10
Answer: A The KE of any object can be computed if the mass (m) and speed (v) are known. Simply use the equation KE=0.5*m*v2 In this case, the 10-N object has a mass of approximately 1 kg (use Fgrav = m*g). The speed is 1 m/s. Now plug and chug to yield KE of approximately 0.5 J.
23. A 4 kg object has a momentum of 12 kg•m/s. The object's speed is ___ m/s. a. 3 b. 4 c. 12 d. 48 e. none of these.
Answer: A This is a relatively simple plug-and-chug into the equation p=m*v with m=4 kg and p=12 kg•m/s.
18. In a physics experiment, two equal-mass carts roll towards each other on a level, low-friction track. One cart rolls rightward at 2 m/s and the other cart rolls leftward at 1 m/s. After the carts collide, they couple (attach together) and roll together with a speed of _____________. Ignore resistive forces. a. 0.5 m/s b. 0.33 m/s c. 0.67 m/s d. 1.0 m/s e. none of these
Answer: A Use 1 kg as the mass of the carts (or any number you wish) and then set the expression for initial total momentum equal to the expression for the final total momentum: (1 kg)*(2) + (1 kg) *(-1) = (1 kg) *v + (1 kg) *v Now solve for v using the proper algebraic steps. (2 kg•m/s) - (1 kg•m/s) = (2 kg) v 1 kg•m/s = (2 kg)v (1 kg•m/s) / (2 kg) = v 0.5 m/s = v
19. Luke Autbeloe stands on the edge of a roof throws a ball downward. It strikes the ground with 100 J of kinetic energy. Luke now throws another identical ball upward with the same initial speed, and this too falls to the ground. Neglecting air resistance, the second ball hits the ground with a kinetic energy of ____ J. a. less than 100 b. 100 c. 200 d. more than 200 e. none of these
Answer: B Quite surprisingly to many, each ball would hit the ground with the same speed. In each case, the PE+KE of the balls immediately after being thrown is the same (they are thrown with the same speed from the same height). Upon hitting the ground, they must also have the same PE+KE. Since the PE is zero (on the ground) for each ball, it stands to reason that their KE is also the same. That's a little physics and a lot of logic - and try not to avoid the logic part by trying to memorize the answer.
21. A 50-kg platform diver hits the water below with a kinetic energy of 5000 Joules. The height (relative to the water) from which the diver dove was approximately ____ meters. a. 5 b. 10 c. 50 d. 100
Answer: B The kinetic energy of the diver upon striking the water must be equal to the original potential energy. Thus, m*g*hi= KEf (50 kg)*(~10 m/s/s)*h = 5000 J So, h = ~10 m
25. Using 1000. J of work, a small object is lifted from the ground floor to the third floor of a tall building in 20.0 seconds. What power was required in this task? a. 20 W b. 50 W c. 100 W d. 1000 W e. 20000 W
Answer: B This is a relatively simple plug-and-chug into the equation P=W/t with W=1000. J and t=20.0 s.
13. Suppose that you're driving down the highway and a moth crashes into the windshield of your car. Which undergoes the greater change is momentum? a. the moth b. your car c. both the same
Answer: C In any collision, there are always four quantities which are the same for both objects involved in the collision. Each object experiences the same force (Newton's third law) for the same amount of time, leading to the same impulse, and subsequently the same momentum change. Only the acceleration and the velocity change can differ for the two objects. The object with the least mass always receives the greatest velocity change and acceleration.
14. Suppose that you're driving down the highway and a moth crashes into the windshield of your car. Which undergoes the greater force? a. the moth b. your car c. both the same
Answer: C In any collision, there are always four quantities which are the same for both objects involved in the collision. Each object experiences the same force (Newton's third law) for the same amount of time, leading to the same impulse, and subsequently the same momentum change. Only the acceleration and the velocity change can differ for the two objects. The object with the least mass always receives the greatest velocity change and acceleration.
15. Suppose that you're driving down the highway and a moth crashes into the windshield of your car. Which undergoes the greater impulse? a. the moth b. your car c. both the same
Answer: C In any collision, there are always four quantities which are the same for both objects involved in the collision. Each object experiences the same force (Newton's third law) for the same amount of time, leading to the same impulse, and subsequently the same momentum change. Only the acceleration and the velocity change can differ for the two objects. The object with the least mass always receives the greatest velocity change and acceleration.
11. In order to catch a ball, a baseball player naturally moves his or her hand backward in the direction of the ball's motion once the ball contacts the hand. This habit causes the force of impact on the players hand to be reduced in size principally because ___. the resulting impact velocity is lessened the momentum change is decreased the time of impact is increased the time of impact is decreased none of these
Answer: C Increasing the time over which the ball's momentum is brought to 0 will decrease the force required to stop it. Suppose a ball is coming at you with 100-units of momentum. An impulse of 100-units would be required to stop the ball. Regardless of how the impulse is accomplished (big F, little t or little F, big t), there must be 100-units of it. Imparting such an impulse over a long time results in a small force.
7. A truck driving along a highway road has a large quantity of momentum. If it moves at the same speed but has twice as much mass, its momentum is ________________. a. zero b. quadrupled c. doubled d. unchanged
Answer: C Momentum is directly related to the mass of the object. So for the same speed, a doubling of mass leads to a doubling of momentum.
20. The firing of a bullet by a rifle causes the rifle to recoil backwards. The speed of the rifle's recoil is smaller than the bullet's forward speed because the ___. a. force against the rifle is relatively small b. speed is mainly concentrated in the bullet c. rifle has lots of mass d. momentum of the rifle is unchanged e. none of these
Answer: C Please don't answer A (for it will make Newton roll over in his grave and he's getting quite tired of that). Perhaps you've heard that "for every action, there is an equal and opposite ...". Choice B is invalid; speed is not something that becomes concentrated or squeezed into an object. Choice D is invalid; ask anyone who's fired a rifle if the rifle is set into motion by the firing of the bullet. (Of course, since it is set in motion, its momentum is not unchanged.) Because of the large mass of the rifle, the acceleration and the recoil speed of the rifle is small.
11. A 1200 kg car and a 2400 kg car are lifted to the same height at a constant speed in a auto service station. Lifting the more massive car requires ____ work. a. less b. the same c. twice as much d. four times as much e. more than 4 times as much
Answer: C The amount of work done by a force to displace an object is found from the equation W = F*d*cos(Theta) The force required to raise the car at constant speed is equivalent to the weight (m*g) of the car. Since the 2400-kg car weighs 2X as much as the 1200-kg car, it would require twice as much work to lift it the same distance.
19. A physics cart rolls along a low-friction track with considerable momentum. If it rolls at the same speed but has twice as much mass, its momentum is ____. a. zero b. four times as large c. twice as large d. unchanged
Answer: C The momentum of an object is calculated as the product of mass and velocity. Thus, the momentum is directly proportional to the mass of the object. If the mass of an object is somehow doubled, the momentum is doubled as well.
24. A 50.0 kg crate is lifted to a height of 2.0 meters in the same time as a 25.0 kg crate is lifted to a height of 4 meters. The rate at which energy is used (i.e., power) in raising the 50.0 kg crate is ____ as the rate at which energy is used to lift the 25.0 kg crate. a. twice as much b. half as much c. the same
Answer: C The power is the rate at which work is done (or energy is used). Power is found by dividing work by time. It requires the same amount of work to do these two jobs (see question #23) and the same amount of time. Thus, the power is the same for both tasks.
21. Two objects, A and B, have the same size and shape. Object A is twice as massive as B. The objects are simultaneously dropped from a high window on a tall building. (Neglect the effect air resistance.) The objects will reach the ground at the same time but object A will have a greater ___. Choose all that apply. a. speed b. acceleration c. momentum d. none of the above quantities will be greater
Answer: C The two objects free-fall at the same rate of acceleration, thus giving them the same speed when they hit the ground. The heavier object however has more momentum since momentum takes into account both the speed and the mass of the object (p=m*v).
17. During a construction project, a 2500 N object is lifted high above the ground. It is released and falls 10.0 meters and drives a post 0.100 m into the ground. The average impact force on the object is ____ Newtons. a. 2500 b. 25000 c. 250,000 d. 2,500,000
Answer: C The use of the work-energy theorem and a simple analysis will yield the solution to this problem. Initially, there is only PE; finally, there is neither PE nor KE; non-conservative work has been done by an applied force upon the falling object. The work-energy equation can be written as follows. PEi + Wnc = 0 PEi = - Wnc m*g*hi = - F*d*cos(Theta) Substituting 2500 N for m*g (2500 N is the weight of the driver, not the mass); 10.0 m for h; 0.100 m for the displacement of the falling object as caused by the upward applied force exerted by the post; and 90 degrees for Theta (the angle between the applied force and the displacement of the falling object) will yield the answer of 250000 N for F.
23. Which requires more work: lifting a 50.0 kg crate a vertical distance of 2.0 meters or lifting a 25.0 kg crate a vertical distance of 4.0 meters? a. lifting the 50 kg crate b. lifting the 25 kg crate c. both require the same amount of work
Answer: C Work involves a force acting upon an object to cause a displacement. The amount of work done is found by multiplying F*d*cos(Theta). The equation can be used for these two motions to find the work. Lifting a 50 kg crate vertically 2 meters W = (~500 N)*(2 m)*cos(0) W = ~1000 N (Note: The weight of a 50-kg object is approximately 500 N; it takes 500 N to lift the object up.) Lifting a 25 kg crate vertically 4 meters W = (~250 N)*(4 m)*cos(0) W = ~1000 N (Note: The weight of a 25-kg object is approximately 250 N; it takes 250 N to lift the object up.)
10. Rank these four objects in increasing order of potential energy, beginning with the smallest. Object AObject BObject CObject Dm = 5.0 kg v = 4.0 m/s h = 2.0 m m = 10.0 kg v = 2.0 m/s h = 3.00 m m = 1.0 kg v = 5.0 m/s h = 5.0 m m = 5.0 kg v = 2.0 m/s h = 4.0 m
Answer: C < A < D < B This is probably best done by performing a calculation of PE and comparing the results. Using the approximation that g = ~10 m/s/s gives much quicker results. Object A: PE = (5.0 kg)•(~10 m/s2)•(2.0 m) = ~100 J Object B: PE = (10.0 kg)•(~10 m/s2)•(3.00 m) = ~300 J Object C: PE = (1.0 kg)•(~10 m/s2)•(5.0 m) = ~50 J Object D: PE = (5.0 kg)•(~10 m/s2)•(4.0 m) = ~200 J The order is evident once the calculations are performed.
20. An object at rest may have __________. a. speed b. velocity c. acceleration d. energy e. all of these
Answer: D An object at rest absolutely cannot have speed or velocity or acceleration. However, an object at rest could have energy if there is energy stored due to its position; for example, there could be gravitational or elastic potential energy.
12. Suppose that Paul D. Trigger fires a bullet from a gun. The speed of the bullet leaving the muzzle will be the same as the speed of the recoiling gun ____. because momentum is conserved because velocity is conserved because both velocity and momentum are conserved only if the mass of the bullet equals the mass of the gun none of these
Answer: D In any collision or explosion involving two objects, the momentum change for each object is the same. So both the bullet and the gun encounter the same momentum change. The momentum change is simply the mass multiplied by the velocity change. Thus, the velocity change would only be the same if their masses were the same. Otherwise, the smaller-mass object receives a greater velocity change.
22. A job is done slowly, and an identical job is done quickly. Both jobs require the same amount of ____, but different amounts of ____. Pick the two words which fill in the blanks in their respective order. a. energy, work b. power, work c. work, energy d. work, power e. power, energy f. force, work g. power, force h. none of these
Answer: D Power refers to the rate at which work is done. Thus, doing two jobs - one slowly and one quickly - involves doing the same job (i.e., the same work and same force) at different rates or with different power.
15. A platform diver weighs 500 N. She steps off a diving board that is elevated to a height of 10 meters above the water. The diver will possess ___ Joules of kinetic energy when she hits the water. a. 10 b. 500 c. 510 d. 5000 e. more than 5000 .
Answer: D The use of the work-energy theorem and a simple analysis will yield the solution to this problem. Initially, there is only PE; finally, there is only KE. Assuming negligible air resistance, the kinetic energy of the diver upon hitting the water is equal to the potential energy of the diver on top of the board. PEi= KEf m*g*hi = KEf Substituting 500 N for m*g (500 N is the weight of the diver, not the mass) and 10 m for h will yield the answer of 5000 J.
9. Rank these four objects in increasing order of kinetic energy, beginning with the smallest. Object AObject BObject CObject Dm = 5.0 kg v = 4.0 m/s h = 2.0 m m = 10.0 kg v = 2.0 m/s h = 3.00 m m = 1.0 kg v = 5.0 m/s h = 5.0 m m = 5.0 kg v = 2.0 m/s h = 4.0 m
Answer: D < C < B < A This is probably best done by performing a calculation of KE and comparing the results: Object A: KE = 0.5•(5.0 kg)•(4.0 m/s)2 = 40. J Object B: KE = 0.5•(10.0 kg)•(2.0 m/s)2 = 20. J Object C: KE = 0.5•(1.0 kg)•(5.0 m/s)2 = ~13 J (12.5 J) Object D: KE = 0.5•(5.0 kg)•(2.0 m/s)2 = 10. J The order is evident once the calculations are performed.
17. Three boxes, X, Y, and Z, are at rest on a table as shown in the diagram at the right. The weight of each box is indicated in the diagram. The net or unbalanced force acting on box Y is _____. a. 4 N down b. 5 N down c. 5 N up d. 10 N up e. zero the boxes are stacked on top of each other same height different width z is in the bottom, longest in width, labeled 10 N y is in the middle, middle in width, labeled 5 N x is on the top, smallest in width, labeled 4 N
Answer: E If an object is at rest, then all the forces acting upon the object must be zero. The net force on any one of the boxes is 0 Newtons. Subsequently, in each case, the support force (which we have called the "normal force throughout this course) acting upwards on any of the boxes must be equal to the force of gravity on that box (i.e., the weight) plus the amount of load exerted from above (which would be equivalent to the weight of the other boxes located above the box). So for box Y, the support force acting upward would be equal to 9 N while the net force is still 0 Newtons. And for box Z, the support force is 19 N, sufficient to balance the 10-N gravitational force plus the 9-N of force resulting from the other two boxes bearing down on it.
14. A 1000-kg car is moving at 40.0 km/hr when the driver slams on the brakes and skids to a stop (with locked brakes) over a distance of 20.0 meters. How far will the car skid with locked brakes if it is traveling at 120. km/hr? a. 20.0 m b. 60.0 m c. 90.0 m d. 120. m e. 180. m
Answer: E When a car skids to a stop, the work done by friction upon the car is equal to the change in kinetic energy of the car. Work is directly proportional to the displacement of the car (skidding distance) and the kinetic energy is directly related to the square of the speed (KE=0.5*m*v2). For this reason, the skidding distance is directly proportional to the square of the speed. So if the speed is tripled from 40 km/hr to 120 km/hr, then the stopping distance is increased by a factor of 9 (from 20 m to 9*20 m; or 180 m). A detailed discussion of the distance-speed squared relationship can be found at The Physics Classroom.
33. Use the work-energy theorem to determine the force required to stop a 988-kg car moving at a speed of 21.2 m/s if there is a distance of 45.7 m in which to stop it. PSYW
Answer: F = 4.86*103 N The work energy theorem can be written as KEi+ PEi+ Wnc= KEf+ PEf The PEi and PEf can be dropped from the equation since they are both 0 (the height of the car is 0 m). The KEf can also be dropped for the same reason (the car is finally stopped). The equation simplifies to KEi+ Wnc= 0 The expressions for KE (0.5*m*v2) and Wnc (F*d*cos[Theta]) can be substituted into the equation: 0.5*m*vi2+ F*d*cos[Theta] = 0 where m=988 kg, vi=21.2 m/s, d=45.7 m, and Theta = 180 degrees. Substituting and solving for F yields 4.86*103 N.
28. Eddy, whose mass is 65.0-kg, climbs up the 1.60-meter high stairs in 1.20 s. Approximate Eddy's power rating. PSYW
Answer: P = 849 Watts Eddy's power is found by dividing the work which he does by the time in which he does it. The work done in elevating his 65.0-kg mass up the stairs is determined using the equation W = F*d*cos(Theta) where F = m*g = 637 N (the weight of the 65.0 kg object), d =1.60 m and Theta = 0 degrees (the angle between the upward force and the upward displacement). Solving for W yields 1019.2 Joules. Now divide the work by the time to determine the power: P = W/t = (1019.2 J)/(1.20 s) =849 Watts
72. In a physics lab, two carts collide elastically on a level, low-friction track. Cart A has a mass of 1.500 kg and is moving east at 36.5 cm/s. Cart B has a mass of 0.500 kg and is moving West at 42.8 cm/s. Determine the post-collision velocities of the two carts.
Answer: vA-after = -3.15 cm/s; vB-after = 76.15 cm/s explanation is too long, just go look at this link if you are confused https://www.physicsclassroom.com/reviews/Momentum-and-Collisions/Momentum-and-Collisions-Review-Answers-4
68. Two billiard balls, assumed to have identical mass, collide in a perfectly elastic collision. Ball A is heading East at 12 m/s. Ball B is moving West at 8.0 m/s. Determine the post-collision velocities of Ball A and Ball B.
Answer: vA-after = -8.0 cm/s; vB-after = 12 cm/s (The - indicates West and the + indicates East) explanation is too long, just go look at this link if you are confused https://www.physicsclassroom.com/reviews/Momentum-and-Collisions/Momentum-and-Collisions-Review-Answers-4
64. In a physics lab, a 0.500-kg cart moving at 36.4 cm/s collides inelastically with a second cart that is initially at rest. The two carts move together with a speed of 21.8 cm/s after the collision. Determine the mass of the second cart.
Answer: ~ 0.335 kg This problem involves a perfectly inelastic collision between two carts. Thus, the post-collision velocity of the two carts are identical. For communication sake, the carts will be referred to as Cart A and Cart B. The given information is: mA= 0.500 kg; vA-before= 36.4 cm/s; vB-before= 0 cm/s; vA-after= 21.8 cm/s; vB-after= 21.8 cm/s The unknown to be solved for in this problem is the mass of Cart B (mB). The solution begins by setting the writing expressions for the total momentum of the system before and after the collision. Before Collision: ptotal-before = (0.500 kg)•(36.4 cm/s) + (mB)•(0 cm/s) After Collision: ptotal-after = (0.500 kg)•(21.8 cm/s) + (mB)•(21.8 cm/s) Assuming momentum conservation, these expressions are set equal to each other and then algebraically manipulated to solve for the unknown (mB). (0.500 kg)•(36.4 cm/s) + (mB)•(0 cm/s) = (0.500 kg)•(21.8 cm/s) + (mB)•(21.8 cm/s) (0.500 kg)•(36.4 cm/s) = (0.500 kg)•(21.8 cm/s) + (mB)•(21.8 cm/s) (0.500 kg)•(36.4 cm/s) - (0.500 kg)•(21.8 cm/s) = (mB)•(21.8 cm/s) (7.30 kg•cm/s) = (mB)•(21.8 cm/s) 0.33486 kg = mB mB = ~0.335 kg
26. Approximate the work required lift a 2.5-kg object to a height of 6.0 meters. PSYW
Answer: ~150 J The work done upon an object is found with the equation W = F*d*cos(Theta) In this case, the d=6.0 m; the F=24.5 N (it takes 24.5 N of force to lift a 2.5-kg object; that's the weight of the object), and the angle between F and d (Theta) is 0 degrees. Substituting these values into the above equation yields W = F*d*cos(Theta) = (24.5 N)*(6 m)*cos(0) =~150 J (147 J)
29. A 51.7-kg hiker ascends a 43.2-meter high hill at a constant speed of 1.20 m/s. If it takes 384 s to climb the hill, then determine ... . PSYW kinetic energy change of the hiker. the potential energy change of the hiker. the work done upon the hiker. the power delivered by the hiker.
Answers: Delta KE = 0 J Delta PE = +21900 J W = +21900 J P = 57.0 Watts a. The speed of the hiker is constant so there is no change in kinetic energy - 0 J. b. The potential energy change can be found by subtracting the initial PE (0 J) from the final PE (m*g*hf). The final potential energy is 21888 J [from (51.7 kg)*(9.8 m/s/s)*(43.2 m)] and the initial potential energy is 0 J. So Delta PE = +21900 J (rounded from 21888 J). c. The work done upon the hiker can be found using the work-energy theorem. The equation reduces to Wnc= PEf (PEi = 0 J since the hiker starts on the ground; and KEi = KEf since the speed is constant; these two terms can be dropped from the equation since they are equal). The final potential energy is 21888 J [from (51.7 kg)*(9.8 m/s/s)*(43.2 m)]. So W = +21900 J (rounded from 21888 J). d. The power of the hiker can be found by dividing the work by the time. P=W/t=(21888 J)/(384 s) =57.0 Watts
30. An 878-kg car skids to a stop across a horizontal surface over a distance of 45.2 m. The average force acting upon the car is 7160 N. Determine ... . PSYW the work done upon the car. the initial kinetic energy of the car. the acceleration of the car. the initial velocity of the car.
Answers: W = -324000 J KEi = +324000 J a = -8.16 m/s/s vi = 27.2 m/s a. The work done upon the car can be found using the equation W = F*d*cos(Theta) where F=7160 N, d=45.2 m, and Theta=180 degrees (the force is in the opposite direction as the displacement). Substituting and solving yields -323632 J (rounded to -324000 J). b. The initial kinetic energy can be found using the work-energy theorem. The equation reduces to KEi+ Wnc= 0 (PEi and PEf = 0 J since the car is on the ground; and KEf = 0 J since the car is finally stopped). Rearrange the equation and it takes the form KEi = -Wnc . So KEi = +324000 J (rounded from +323632 J). c. The acceleration of the car can be found using Newton's second law of motion: Fnet = m*a The friction force is the net force (since the up and down forces balance) and the mass is 878 kg. Substituting and solving yields a = -8.16 m/s/s. d. The initial velocity of the car can be found using the KE equation: KE = 0.5*m*v2 where m=878 kg and KEi=323632 J. Substituting and solving for velocity (v) yields v = 27.2 m/s. (A kinematic equation could be also used to find the initial velocity.)
32. A 65.8-kg skier accelerates down an icy hill from an original height of 521 meters. Use the work-energy theorem to determine the speed at the bottom of the hill if... a. ... no energy is lost or gained due to friction, air resistance and other non-conservative forces. PSYW b. ... 1.40*105 J of energy are lost due to external forces. PSYW Answers: (a) v = 101 m/s; (b) v = 77.2 m/s
Answers: (a) v = 101 m/s; (b) v = 77.2 m/s a. Use the work energy theorem: KEi+ PEi+ Wnc= KEf+ PEf The PEf can be dropped from the equation since the skier finishes on the ground at zero height. The KEi can also be dropped since the skier starts from rest. The Wnc term is dropped since it is said that no work is done by non-conservative (external) forces. The equation simplifies to PEi= KEf The expressions for KE (0.5*m*v2) and PE (m*g*h) can be substituted into the equation: m*g*h = 0.5*m*vf2 where m=65.8 kg, h=521 m, g=9.8 m/s/s. Substituting and solving for vf yields 101 m/s. b. This equation can be solved in a similar manner, except that now the Wext term is -140000 J. So the equation becomes m*g*h - 140000 J = 0.5*m*vf2 Now substituting and solving for vf yields 77.2 m/s.
10. It is NOT possible for a rocket to accelerate in outer space because ____. List all that apply. there is no air in space there is no friction in space there is no gravity in outer space ... nonsense! Rockets do accelerate in outer space.
D Rockets accelerate in outer space by means of Newton's third law of motion. It does not matter that there is no air outside of the rocket. Rockets produce their own gas by burning fuels. The combustion of rocket fuels produces gaseous products. The rocket's thrusters push these gases backwards (or rightwards, or leftwards, or ...) and the gases push the rocket forwards (or leftwards, or rightwards, or ...). Thus, rockets indeed can and do accelerate in outer space.
The kinetic energy of an object is dependent upon the weight and the speed of an object.
FALSE (sort of) - Kinetic energy depends upon mass and speed. Two objects of the same mass could have different weights if in a different gravitational field; so it is not appropriate to say that kinetic energy depends upon weight.
The Newton•meter is a unit of power.
FALSE - A N•m is a Joule and that is a unit of work (not power). Think force (N) times distance (m); that's work (J).
Faster moving objects always have a greater kinetic energy.
FALSE - Faster moving objects would have more kinetic energy than other objects of the same mass. However, another object could have less speed and make up for this lack of speed in terms of a great
An eraser is tied to a string; a person holds the string and applies a tension force as the eraser is moved in a circle at constant speed. This is an example of work being done.
FALSE - For uniform circular motion, the force acts perpendicular to the direction of the motion and so the force never does any work upon the object.
A force acts upon an object at a 90-degree angle to the direction that it is moving. This force is doing negative work upon the object.
FALSE - If a force acts at a 90-degree angle to the direction of motion, then the force does not do any work at all. Negative work is done when there is a component of force opposite the direction of motion.
A falling object always gains kinetic energy as it falls.
FALSE - If an object is falling at a constant velocity (i.e., the air resistance force equals the downward force of gravity), then there is not an increase in kinetic energy. It is true however that free-falling objects always increase their kinetic energy as they fall.
If an object is at rest, then it does not have any kinetic energy. TRUE - Kinetic energy depends upon speed. If there is no speed (the object is at rest), then there is no kinetic energy.
FALSE - If an object is on the ground, then it does not have potential energy (relative to the ground).
If an object is on the ground, then it does not have any kinetic energy.
FALSE - If an object is on the ground, then it does not have potential energy (relative to the ground).
Kinetic energy is the form of mechanical energy which depends upon the position of an object.
FALSE - Kinetic energy depends upon the speed of the object; potential energy depends upon the position of the object.
An object has a kinetic energy of 40 J. If its mass were twice as much, then its kinetic energy would be 80 J.
FALSE - Kinetic energy is directly related to the square of the speed of an object. So a doubling of the speed would result in a quadrupling of the kinetic energy - the new KE would be 160 J
More massive objects always have a greater kinetic energy.
FALSE - More massive objects would have more kinetic energy than other objects with the same speed. However, another object could have less mass and make up for this lack of mass in terms of a greater speed.
f. Superman applies a force on a truck to prevent it from moving down a hill. This is an example of work being done.
FALSE - Since Superman does not cause a displacement, no work is done; he is merely holding the car to prevent its descent down the hill.
If work is done on an object by a non-conservative force, then the object will either gain or lose kinetic energy.
FALSE - Such an object will definitely gain or lose mechanical energy but not necessarily kinetic energy.
A 1-kg object is accelerated from rest to a speed of 2.0 m/s. This object gains 4.0 Joules of kinetic energy.
FALSE - The kinetic energy increases from 0 J to 2 J (0.5•1•22); that's an increase by 2 J.
An upward force is applied to a bucket as it is carried 20 m across the yard. This is an example of work being done.
FALSE - The upward force does not cause the horizontal displacement so this is a NON-example of work.
A 60-kg boy runs up a 2.0 meter staircase in 1.5 seconds. His power is approximately 80 Watt.
FALSE - The work would be (m•g)•d or approximately 1200 J. The power is work divided by time - 1200 J/1.5 s = 800 W.
An individual force does NOT do positive work upon an object if the object is moving at constant speed.
FALSE - There are many instances in which an individual force does positive work and yet the object maintains a constant speed. Consider a force applied to lift an object at constant speed. The force does positive work. Consider a car moving at constant speed along a level surface. The force of the road on the tires does positive work while air resistance does and equal amount of negative work.
A force acts upon an object to push the object along a surface at constant speed. By itself, this force must NOT be doing any work upon the object.
FALSE - This is clearly work - a force is causing an object to be displaced.
Powerful people or powerful machines are simply people or machines which always do a lot of work.
FALSE - This is not always the case. A machine can do a lot of work but if it fails to do it rapidly, then it is not necessarily powerful. In fact two machines can do the same task (and therefore the same work), yet they can have drastically different power ratings.
If person A and person B do the same job but person B does it faster, then person A does more work but person B has more power.
FALSE - Vice versa. If two people do the same job, then they're doing the same amount of work. The person who does it fastest generates more power.
A Watt is the standard metric unit of work.
FALSE - Watt is the standard metric unit of power; Joule is the standard metric unit of energy.
Object A has a mass of 1 kg and a speed of 2 m/s. Object B has a mass of 2 kg and a speed of 1 m/s. Objects A and B have the same kinetic energy.
FALSE - When it comes to kinetic energy, speed is doubly important (recall v2). So in this case, object A would have more kinetic energy. Doing the calculation yields 2 J for object A and 1 J for object B.
Work is a time-based quantity; it is dependent upon how fast a force displaces an object.
FALSE - Work is not dependent on how rapidly the force displaces an object; power is time-based and calculated by force multiplied by speed.
Units of work would be equivalent to a Newton times a meter.
TRUE - A N•m is equal to a Joule.
potential energy formula
PE=mgh
3. Which of the following statements are true about impulse? a. Impulse is a force. b. Impulse is a vector quantity. c. An object which is traveling east would experience a westward directed impulse in a collision. d. Objects involved in collisions encounter impulses. e. The Newton is the unit for impulse. f. The kg•m/s is equivalent to the units on impulse. g. An object which experiences a net impulse will definitely experience a momentum change. h. In a collision, the net impulse experienced by an object is equal to its momentum change. i. A force of 100 N acting for 0.1 seconds would provide an equivalent impulse as a force of 5 N acting for 2.0 seconds.
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 faster-moving 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 impulse-momentum 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.
2. Which of the following are true about the relationship between momentum end energy? a. Momentum is a form of energy. b. If an object has momentum, then it must also have mechanical energy. c. If an object does not have momentum, then it definitely does not have mechanical energy either. d. Object A has more momentum than object B. Therefore, object A will also have more kinetic energy. e. Two objects of varying mass have the same momentum. The least massive of the two objects will have the greatest kinetic energy.
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.
a. Moving objects cannot have potential energy. b. Potential energy is the energy stored in an object due to its position. c. Both gravitational and elastic potential energy are dependent upon the mass of an object. d. The gravitational potential energy of an object is dependent upon the mass of the object. e. If the mass of an elevated object is doubled, then its gravitational potential energy will be doubled as well. f. Gravitational potential energy is lost as objects free-fall to the ground. g. The higher that an object is, the more potential energy which it will have. h. The unit of measurement for potential energy is the Joule. i. A 1-kg mass at a height of 1 meter has a potential energy of 1 Joule. j. A 1-kg object falls from a height of 10 m to a height of 6 m. The final potential energy of the object is approximately 40 J. k. If work is done on an object by a non-conservative force, then the object will either gain or lose potential energy.
a. FALSE - Potential energy has nothing to do with speed; an object could be moving at an elevated position. It is this elevation above zero level which gives an object potential energy. b. TRUE - This is the definition of potential energy. c. FALSE - Gravitational potential energy is dependent upon the mass of the object (PEgrav = m•g•h) but elastic potential energy is dependent upon the spring constant and the compression or stretch length of the spring (PEelastic = 0.5•k•x2). d. TRUE - The equation states that PEgrav = m•g•h; PE is dependent upon mass. e. TRUE - The equation states that PEgrav = m•g•h; if the h is doubled, then the PE will be doubled as well. f. TRUE - As objects free-fall, the height (h) decreases; subsequently, the PE decreases. g. TRUE - The equation states that PEgrav = m•g•h; PE is directly related to height. h. TRUE - The Joule (abbrev. J) is the standard metric unit of energy - all forms of energy. i. FALSE - The final potential energy is calculated as PE = m•g•h = (1 kg)•(~10 m/s/s)•(1 m) = ~10 J. j. FALSE - The final potential energy is calculated as PE = m•g•h = (1 kg)•(~10 m/s/s)•(6 m) = ~60 J; the loss in potential energy during this 4-m fall is -40 J. k. FALSE - The object will either gain or lose mechanical energy, but not necessarily potential energy.
5. Which of the following statements are true about elastic and inelastic collisions? aPerfectly elastic and perfectly inelastic collisions are the two opposite extremes along a continuum; where a particular collision lies along the continuum is dependent upon the amount kinetic energy which is conserved by the two objects. bMost collisions tend to be partially to completely elastic. cMomentum is conserved in an elastic collision but not in an inelastic collision. dThe kinetic energy of an object remains constant during an elastic collision. eElastic collisions occur when the collision force is a non-contact force. fMost collisions are not inelastic because the collision forces cause energy of motion to be transformed into sound, light and thermal energy (to name a few). gA ball is dropped from rest and collides with the ground. The higher that the ball rises upon collision with the ground, the more elastic that the collision is. hA moving air track glider collides with a second stationary glider of identical mass. The first glider loses all of its kinetic energy during the collision as the second glider is set in motion with the same original speed as the first glider. Since the first glider lost all of its kinetic energy, this is a perfectly inelastic collision. iThe collision between a tennis ball and a tennis racket tends to be more elastic in nature than a collision between a halfback and linebacker in football.
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 non-contact 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 non-contact 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 post-collision velocity is high compared to the pre-collision 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 ball-racket collision tends to be more elastic.
4. Which of the following statements are true about collisions? aTwo colliding objects will exert equal forces upon each other even if their mass is significantly different. bDuring a collision, an object always encounters an impulse and a change in momentum. cDuring a collision, the impulse which an object experiences is equal to its velocity change. dThe velocity change of two respective objects involved in a collision will always be equal. eWhile individual objects may change their velocity during a collision, the overall or total velocity of the colliding objects is conserved. fIn a collision, the two colliding objects could have different acceleration values. gIn a collision between two objects of identical mass, the acceleration values could be different. hTotal momentum is always conserved between any two objects involved in a collision. iWhen a moving object collides with a stationary object of identical mass, the stationary object encounters the greater collision force. jWhen a moving object collides with a stationary object of identical mass, the stationary object encounters the greater momentum change. kA moving object collides with a stationary object; the stationary object has significantly less mass. The stationary object encounters the greater collision force. lA moving object collides with a stationary object; the stationary object has significantly less mass. The stationary object encounters the greater momentum change.
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 action-reaction. 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.
1. Which of the following statements are true about momentum? a.Momentum is a vector quantity. b.The standard unit on momentum is the Joule. c.An object with mass will have momentum. d.An object which is moving at a constant speed has momentum. e.An object can be traveling eastward and slowing down; its momentum is westward. f.Momentum is a conserved quantity; the momentum of an object is never changed. g.The momentum of an object varies directly with the speed of the object. h..Two objects of different mass are moving at the same speed; the more massive object will have the greatest momentum. i.A less massive object can never have more momentum than a more massive object. j.Two identical objects are moving in opposite directions at the same speed. The forward moving object will have the greatest momentum. k.An object with a changing speed will have a changing momentum.
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.
a. The total amount of mechanical energy of an object is the sum of its potential energy and the kinetic energy. b. Heat is a form of mechanical energy. c. The mechanical energy of an object is always conserved. d. When non-conservative forces do work, energy is transformed from kinetic to potential (or vice versa), but the total mechanical energy is conserved. e. A bowling ball is mounted from a ceiling by way of a strong cable. It is drawn back and released, allowed to swing as a pendulum. As it swings from its highest position to its lowest position, the total mechanical energy is mostly conserved. f. When a friction force does work on an object , the total mechanical energy of that object is changed. g. The total mechanical energy of an object remains constant if the only forces doing work on the object are conservative forces. h. If an object gains mechanical energy, then one can be certain that a non-conservative force is doing work.
a. TRUE - This is the definition of mechanical energy. b. FALSE - Heat or thermal energy is a non-mechanical form of energy. Potential and kinetic energy are the only forms of mechanical energy. c. FALSE - The mechanical energy of an object is only conserved if non-conservative forces do not do work upon the object. d. FALSE- If a non-conservative force does work upon an object, then the total mechanical energy of that object is changed. Energy will not be conserved. e. TRUE - Tension does not do work upon the object and so the total mechanical energy is conserved. The presence of air resistance (a non-conservative force) does a little work and so one might notice a very slight change in mechanical energy. f. TRUE - Friction is a non-conservative force and thus alters the total mechanical energy of an object. g. TRUE - This is the conservation of energy principle and one that you need to firmly understand. h. TRUE - If there is any change in the total mechanical energy of an object (whether a gain or a loss), then you know for certain that there is a non-conservative force doing work.
An object at rest may have __________. a. speed b. velocity c. acceleration d. energy e. all of these
d
Kinetic energy is a scalar quantity.
h. TRUE - Kinetic energy is directly related to the mass of an object.
# 34-37 you need to look at this link to do.
https://www.physicsclassroom.com/reviews/Work-and-Energy/Work-and-Energy-Review-Answers
a. Positive Work b. Negative Work c. No Work In baseball, the catcher exerts an abrupt applied force upon the ball to stop it in the catcher's mitt.
negative
a. Positive Work b. Negative Work c. No Work Near the end of the Shockwave ride, a braking system exerts an applied force upon the coaster car to bring it to a stop.
negative
a. Positive Work b. Negative Work c. No Work The force of friction acts upon a baseball player as he slides into third base.
negative
a. Positive Work b. Negative Work c. No Work A busy spider hangs motionless from a silk thread, supported by the tension in the thread.
no work
a. Positive Work b. Negative Work c. No Work A pendulum bob swings from its highest position to its lowest position under the influence of the force of gravity.
positive
a. Positive Work b. Negative Work c. No Work In a physics lab, an applied force is exerted parallel to a plane inclined at 30-degrees in order to displace a cart up the incline
positive
a. Positive Work b. Negative Work c. No Work Rusty Nales uses a hammer to exert an applied force upon a stubborn nail to drive it into the wall.
positive
a. Positive Work b. Negative Work c. No Work A cable is attached to a bucket and the force of tension is used to pull the bucket out of a well.
postive