Exam 2 PC

A car of mass M, traveling with a velocity V, strikes a parked station wagon, whose mass is 2M. The bumpers lock together in this head-on inelastic collision. What fraction of the initial kinetic energy is lost in this collision? A) 1/2 B) 1/4 C) 2/3 D) 1/9 E) 1/3

c

A skier, of mass 60. kg, pushes off the top of a frictionless hill with an initial speed of 4.0 m/s. How fast will she be moving after dropping 10. m in elevation? A) 15. m/s B) 49. m/s C) 0.20 km/s D) 0.15 km/s E) 10. m/s

a

Matthew pulls his little sister Sarah in a sled on an icy surface (assume no friction), with a force of 60.0 Newtons at an angle of 37.0° upward from the horizontal. If he pulls her a distance of 12.0 m, the work he does is A) 720 J B) 185 J C) 0.333 kJ D) 433 J E) 575 J

e

Refer to Fig. 4-13. If the train has an acceleration of 5.50 m/ , then the tension force in the coupling between the middle car and the engine car is A) 8.25 kN. B) 11.0 kN. C) 5.50 kN. D) 27.5 kN. E) 16.5 kN.

e

Refer to Fig. 4-13. The wheels of the engine are pushing back with what force? A) 550. N B) 16.5 kN C) 5.50 kN D) 11.0 kN E) 27.5 kN

e

Stacy (S) and David (D) are having a tug-of-war by pulling on opposite ends of a 5.0 kg rope. Stacy pulls with a 15. N force. What is David's force if the rope accelerates toward Stacy at 2.0 m/ ? A) 15 N B) 50 N C) 3 N D) 25 N E) 5 N

e

A 16-kg fish is weighed with two spring scales, each of negligible weight, as shown in Fig. 4-2. What will be the readings on the scales? A) The sum of the two readings will be 32 kg. B) Each scale will show a reading greater than zero and less than 16 kg, but the sum of the two readings will be 16 kg. C) The bottom scale will read 16 kg, and the top scale will read zero. D) The top scale will read 16 kg, and the bottom scale will read zero. E) Each scale will read 8 kg.

a

A 20-ton truck collides with a 1500-lb car and causes a lot of damage to the car. A) The force of collision on the truck is equal to the force of collision on the car. B) The car did not slow down during the collision. C) The force of collision on the truck is greater then the force of collision on the car. D) The force of collision on the truck is smaller than the of collision force on the car. E) The truck did not slow down during the collision.

a

A 200-g mass attached to the end of a spring causes it to stretch 5.0 cm. If another 200-g mass is added to the spring, the potential energy of the spring will be A) 4 times as much. B) 3 times as much. C) times as much. D) twice as much. E) the same.

a

A 60.0-kg mass person wishes to push a 120-kg mass box across a level floor. The coefficient of static friction between the person's shoes and the floor is 0.700. What is the maximum coefficient of static friction between the box and the floor such that the person can push horizontally on the box and cause it to start moving? A) 0.350 B) 0.667 C) 0.700 D) 0.333 E) 0.500

a

A golf club exerts an average force of 1000 N on a 0.045-kg golf ball which is initially at rest. The club is in contact with the ball for 1.8 ms. What is the speed of the golf ball as it leaves the tee? A) 40 m/s B) 45 m/s C) 50 m/s D) 30 m/s E) 35 m/s

a

An object is moving with constant velocity in a straight line. Which of the following statements is true? a. the net force on the object is zero b. a constant force is being applied in the direction opposite of motion c. there is no frictional force acting on the object d. a constant force is being applied in the direction of motion e. there are no forces acting on the object

a

An object of mass 10.0 kg is initially at rest. A 100 N force causes it to move horizontally through a distance of 6.00 m. What is the change in the kinetic energy of this object? A) 600 J B) 1000 J C) 0 J D) 60.0 J E) 200 J

a

Car J moves twice as fast as car K, and car J has half the mass of car K. The kinetic energy of car J, compared to car K is A) 2 to 1. B) 1 to 2. C) the same. D) to 1. E) 4 to 1.

a

How much energy is needed to change the speed of a 1600 kg sport utility vehicle from 15.0 m/s to 40.0 m/s? A) 1.10 MJ B) 0.960 MJ C) 10.0 kJ D) 40.0 kJ E) 20.0 kJ

a

If both the mass and the velocity of a ball are tripled, the kinetic energy is increased by a factor of A) 27. B) 18. C) 6. D) 9. E) 81.

a

If you blow up a balloon, and then release it, the balloon will fly away as the air rushes out. This is an illustration of: A) Newton's Third Law. B) Newton's Second Law. C) Newton's Law of Universal Gravitation. D) Galileo's Law of Inertia. E) Newton's First Law.

a

If you push a 4-kg mass with the same force that you push a 10-kg mass from rest, then A) the 4-kg mass accelerates 2.5 times faster than the 10-kg mass. B) the 10-kg mass accelerates 2.5 times faster than the 4-kg mass. C) the 4-kg mass accelerates 4 times faster than the 10-kg mass. D) both masses accelerate at the same rate. E) the 10-kg mass accelerates 4 times faster than the 4-kg mass.

a

King Kong falls from the top of the Empire State Building, through the air (air friction is present), to the ground below. How does his kinetic energy (K) just before striking the ground compare to his potential energy (U) at the top of the building? A) K is less than U. B) K is greater than U. C) K is equal to U. D) It is impossible to tell.

a

Two equal mass balls (one blue and the other gold) are dropped from the same height, and rebound off the floor. The blue ball rebounds to a higher position. Which ball is subjected to the greater magnitude impulse during its collision with the floor? A) the blue ball B) It's impossible to tell since the time intervals and forces are unknown. C) Both balls were subjected to the same magnitude impulse. D) the gold ball

a

Work done by STATIC FRICTION is always A) zero. B) positive. C) along the surface. D) perpendicular to the surface. E) negative.

a

A decoration, of mass M, is suspended by a string from the ceiling inside an elevator. The elevator is traveling UPWARD with a constant speed. The tension in the string is A) greater than Mg. B) equal to Mg. C) less than Mg. D) impossible to tell without knowing the speed. E) impossible to tell without knowing the decoration mass.

b

10) You try to pull an object by tugging on a rope attached to the object with a force . The object does not move at all. What does this imply A) The inertia of the object prevents it from accelerating. B) There are also one or more other forces that act on the object with a sum - . C) The rope is not transmitting the force to the object. D) There are no other forces acting on the object. E) The object has reached its natural state of rest and can no longer be set into motion.

b

A 10. kg mass, hung onto a spring, causes the spring to stretch 2.0 cm. The spring constant is A) 20. N/m B) 49 N/cm C) 0.20 N/cm D) 5.0 N/cm E) 0.0020 N/cm

b

A 42.0 kg block of ice slides down the plane incline 34.0° in Fig. 4-14. Assuming friction is negligible, what is the acceleration of the block down the incline? A) 8.12 m/ B) 5.48 m/ C) 9.80 m/ D) 6.61 m/ E) 2.73 m/

b

A 6.00-kg block is in contact with a 4.00-kg block on a frictionless surface as shown in Fig. 4-11. The 6.00-kg block is being pushed by a 20.0-N force toward the 4.00-kg block. What is the magnitude of the force of the 6.00-kg block on the 4.00-kg block? A) 6.00 N B) 10.0 N C) 8.00 N D) 4.00 N E) 12.0 N

b

A 60. gram toy rocket achieves a speed of 80. m/s after 3.0 s, when fired straight up. What is the average total force on the rocket during the 3 s? A) 2.2 N B) 1.6 N C) 3.2 N D) 3.4 N E) 1.2 N

b

A container of water is lifted vertically 3.0 m, then returned to its original position. If the total weight is 30. N, how much work was done? A) 0.18 kJ B) No work was done. C) 45 J D) 0.90 kJ E) 90 J

b

A small car meshes with a large truck in a head-on collision. Which of the following statements concerning the magnitude of the average collision force is correct? A) The small car experiences the greater average force. B) The small car and the truck experience the same average force. C) The truck experiences the greater average force. D) It is impossible to tell since the masses and velocities are not given.

b

A spring is characterized by a spring constant of 60. N/m. How much potential energy does it store, when stretched by 1.0 cm? A) 6.0 μJ B) 0.003 J C) 0.3 J D) 600. J E) 60. J

b

Assuming negligible friction, what spring constant would be needed by the spring in a "B-B gun" to fire a 10. gram pellet to a height of 100 meters if the spring is initially compressed 10. cm? A) 200. N/m B) 20. N/cm C) 2.0 × N/cm D) 2.0 × N/m E) 20. N/m

b

When you sit on a chair, the reaction to your weight is A) your push down on the chair. B) the Earth being pulled up. C) the floor pushing up on the chair. D) the chair pushing on you. E) zero if in equilibrium.

b

Which of the graphs in Fig. 5-1 illustrates Hooke's Law? A) graph a B) graph b C) graph c D) graph d E) none of the above

b

A Ping-Pong ball moving East at a speed of 4 m/s collides with a stationary bowling ball. The Ping-Pong ball bounces back to the West, and the bowling ball moves very slowly to the East. Which object experiences the greater magnitude impulse during the collision? A) It's impossible to tell since the velocities after the collision are unknown. B) the Ping-Pong ball C) Neither; both experienced the same magnitude impulse. D) the bowling ball

c

30) A brick and a feather fall to the Earth at their respective terminal velocities. Which object experiences the greater force of air friction? A) Neither, both experience the same amount of air friction force. B) the feather C) the brick

c

A 2.0 kg mass moving to the East at a speed of 4.0 m/s collides head-on in an inelastic collision with a stationary 2.0 kg mass. How much kinetic energy is lost during this collision? A) 2.0 J B) 4.0 J C) 8.0 J D) 16. J E) zero

c

A small bomb, of mass 10. kg, is moving toward the North with a velocity of 5.0 m/s. It explodes into three fragments: a 5.0 kg fragment moving West with a speed of 8.0 m/s; a 4.0 kg fragment moving East with a speed of 10. m/s; and a third fragment with a mass of 1.0 kg. What is the velocity of the third fragment? (Neglect air friction.) A) 50.m/s North B) zero C) 4.0 m/s North D) 5.0 m/s South E) 40 m/s North

c

Automobile air bags reduce what during a collision? A) speed of the automobile B) the kinetic energy transferred to the passenger C) the forces exerted upon the passenger D) the impulse exerted upon the passenger

c

Batter up! Your bat hits the ball pitched to you with a 1500-N instantaneous force. The ball hits the bat with an instantaneous force, whose magnitude is A) somewhat less than 1500 N. B) somewhat greater than 1500 N. C) exactly equal to 1500 N. D) essentially zero.

c

If the net work done on an object is positive, then the object's kinetic energy A) is zero. B) remains the same. C) increases. D) decreases. E) cannot be determined without knowing the object's mass

c

Planning to elope with her boyfriend, Janice slides down a rope from her fourth story window. As she slides down the rope, she tightens harder on the rope which of course increases the tension in the rope. When the upward tension in the rope equals Janice's weight A) Janice will speed up. B) the rope will break. C) Janice will continue down at constant speed. D) Janice will stop moving down the rope. E) Janice will slow down.

c

Suppose a bug spatters upon your windshield as you drive down the road. Which sustains the greater change of momentum? A) the bug B) insufficient information C) both the same D) the car

c

The following four forces act on a 4.00 kg object: F1 = 300 N east F2 = 700 N north F3 = 500 N west F4 = 600 N south What is the acceleration of the object? A) 300 N in a direction 26.6° north of west B) 224 N in a direction 63.4° north of west C) 224 N in a direction 26.6° north of west D) 300 N in a direction 63.4° north of west E) 2100 N in a direction 26.6° north of west

c

To push a piece of heavy furniture across the carpet usually takes more force to get it moving than it takes to keep is moving. This is because A) of Newton's second law. B) of Newton's first law. C) the static coefficient of friction is larger than the kinetic coefficient. D) of Newton's third law. E) the kinetic coefficient of friction is larger than the static coefficient.

c

Two identical masses are attached by a light string that passes over a small pulley, as shown in Fig. 4-3. The table and the pulley are frictionless. The masses are moving A) with an acceleration greater than g. B) with an acceleration equal to g. C) with an acceleration less than g. D) at constant speed.

c

Two toy cars (16 kg and 2 kg) are released simultaneously on an inclined plane that makes an angle of 30° with the horizontal. Which statement best describes their acceleration after being released? A) The 16-kg car accelerates 8 times faster than the 2-kg car. B) The 2-kg car accelerates 8 times faster than the 16-kg car. C) Both cars accelerate at a rate of g sin(30°). D) Both cars accelerate at a rate of 8∗g. E) Both cars accelerate at a rate of 0.866 g.

c

You are standing in a moving bus, and you suddenly fall backward. You can imply from this that the bus'. A) velocity decreased. B) speed remained the same, but it's turning to the right. C) velocity increased. D) the bus stopped. E) speed remained the same, but it's turning to the left

c

You throw a ball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down. A) Work up is +, and the work down is -. B) Work up is -, and the work down is -. C) Work up is -, and the work down is +. D) Work up is +, and the work down is +.

c

Is it possible for a system to have negative potential energy? A) Yes, as long as the total energy is negative. B) No, because the kinetic energy of a system must equal its potential energy. C) No, because this would have no physical meaning. D) Yes, as long as the total energy is positive. E) Yes, since the choice of the zero of potential energy is arbitrary.

e

A 100 kg football linebacker moving at 2 m/s tackles head-on an 80 kg halfback running 3 m/s. Neglecting the effects due to digging in of cleats A) neither player will drive the other backward. B) this is a simple example of an elastic collision. C) the linebacker will drive the halfback backward. D) the halfback will drive the linebacker backward.

d

A child's toy is suspended from the ceiling by means of a string. The Earth pulls downward on the toy with its weight force of 8 N. If this is the "action force," what is the "reaction force"? A) the string pulling upward on the toy with an 8-N force B) the string pulling downward on the ceiling with an 8-N force C) the toy pushing downward on the Earth with an 8-N force D) the toy pulling upward on the Earth with an 8-N force E) the ceiling pulling upward on the string with an 8-N force

d

A handball of mass 0.10 kg, traveling horizontally at 25. m/s, strikes a wall and rebounds at 19. m/s. What is the change in the momentum of the ball? A) 1.8 N-s B) 4.4 N-s C) 72 N-s D) 5.4 N-s E) 1.2 N-s

d

A leaf falls from a tree. Compare its kinetic energy K to its potential energy U. A) K decreases, and U decreases. B) K decreases, and U increases. C) K and U remain constant. D) K increases, and U decreases. E) K increases, and U increases.

d

A person carries a mass of 10 kg and walks along the +x-axis for a distance of 100m with a constant velocity of 2 m/s. What is the work done by this person? A) 1000 J B) 200 J C) 20 J D) 0 J E) None of the other choices is correct.

d

A toolbox, of mass M, is resting on a flat board, as shown in Fig. 4-5. One end of the board is lifted up until the toolbox just starts to slide. The angle θ that the board makes with the horizontal, for this to occur, depends on the A) mass, M. B) coefficient of kinetic friction, . C) acceleration of gravity, g. D) coefficient of static friction, . E) all of the above quantities.

d

An arrow is shot straight up. At the top of its path, the net force acting on it is A) greater than its weight. B) greater than zero, but less than its weight. C) instantaneously equal to zero. D) equal to its weight. E) horizontal.

d

Car A (mass = 1000 kg) moves to the right along a level, straight road at a speed of 6.0 m/s. It collides directly with car B (mass = 200 kg) in a completely inelastic collision. What is the momentum after the collision if car B was initially at rest? A) zero B) 8.0 KN-s to the left C) 2.0 KN-s to the right D) 6.0 KN-s to the right E) 10. KN-s to the right

d

Two cardboard boxes full of books are in contact with each other on a table, as shown in Fig. 4-4. Box H has twice the mass of box G. If you push on box G with a horizontal force F, then box H will experience a net force of A) 2 F. B) F. C) 3/2 F. D) 2/3 F. E) 3 F.

d

You and your friend want to go to the top of the Eiffel Tower. Your friend takes the elevator straight up. You decide to walk up the spiral stairway, taking longer to do so. Compare the gravitational potential energy (U) of you and your friend, after you both reach the top, assuming that you and your friend have equal masses. A) Your U is greater than your friend's U, because you traveled a greater distance in getting to the top. B) Your friend's U is greater than your U, because she got to the top faster. C) It is impossible to tell, since the times and distances are unknown. D) Both of you have the same amount of potential energy.

d

You fall, while skiing, and one ski (of weight W) loosens and slides down an icy slope (assume no friction), which makes an angle θ with the horizontal. The force that pushes it down along the hill is A) W cos θ. B) W tan θ. C) W. D) W sin θ. E) zero; it moves with constant velocity

d

A 4.0 kg box of fruit slides 8.0 m down a ramp, inclined at 30.° from the horizontal. If the box slides at a constant velocity of 5.0 m/s, the work done by gravity is A) -0.16 kJ. B) -78. J. C) zero. D) +78. J. E) 0.16 kJ.

e

A ball, of mass 100. g, is dropped from a height of 12. m. Its momentum when it strikes the ground is A) 3.3 kg∙m/s. B) 1.8 kg∙m/s. C) 4.8 kg∙m/s. D) 2.4 kg∙m/s. E) 1.5 kg∙m/s.

e

If you pitch a baseball with twice the kinetic energy you gave it in a previous pitch, the magnitude of its momentum is A) the same. B) 4 times as much. C) doubled. D) 2 times as much. E) times as much.

e

If you push twice as hard against a stationary brick wall, the amount of work you do A) is cut in half. B) doubles. C) remains constant but non-zero. D) quadruples. E) remains constant at zero.

e

Suppose several forces are acting upon a mass m. The in = m refers A) any particular one of the forces. B) the arithmetic sum of all the forces. C) the arithmetic mean of all the forces. D) the vector sum of all the forces. E) the force of friction acting upon the mass.

e

When a cannon fires a cannonball, the cannon will recoil backward because the A) energy of the cannonball and cannon is conserved. B) momentum of the cannon is conserved. C) momentum of the cannon is greater than the energy of the cannonball. D) energy of the cannon is greater than the energy of the cannonball. E) momentum of the cannonball and cannon is conserved.e

e

You are standing in a moving bus, facing forward, and you suddenly move forward as the bus comes to an immediate stop. What force caused you to move forward? A) normal force due to your contact with the floor of the bus B) force due to static friction between you and the floor of the bus C) force of gravity D) force due to kinetic friction between you and the floor of the bus E) no forces were responsible for your fall.

e

You slam on the brakes of your car in a panic, and skid a certain distance on a straight, level road. If you had been traveling twice as fast, what distance would the car have skidded, under the same conditions? A) It would have skidded half as far. B) It would have skidded twice as far. C) It would have skidded times farther. D) It is impossible to tell from the information given. E) It would have skidded 4 times farther.

e