Physics chapter 7

A ball of mass 400 g moving toward the east with a speed of 3.70 m/s collides head-on with a 200 g ball sitting at rest. The collision is perfectly elastic. (a) Determine the velocity of the first ball after the collision. (b) Determine the velocity of the second ball after the collision. (c) Is kinetic energy conserved in this collision?

(a) 1.2 m/s toward the east (b) 4.9 m/s toward the east (c) Yes, it is an elastic collision.

A 15-g bullet traveling 213 m/s in a vertical direction buries itself in a 2.4-kg block of wood at rest directly above it. As a result, the bullet/block combination moves vertically upward. (a) Determine the velocity of the bullet/block combination at the point of impact. (b) Determine the maximum height reached by the bullet/block combination. (c) Is kinetic energy conserved in this collision?

(a) 1.3 m/s (b) 0.089 m (c) No, this is an inelastic collision.

A 10.0-g bullet moving at 300 m/s is fired into a 1.00-kg block at rest. The bullet emerges (the bullet does not get embedded in the block) with half of its original speed. What is the velocity of the block right after the collision? A) 1.50 m/s B) 2.97 m/s C) 3.00 m/s D) 273 m/s

A

A 3.0-kg mass is positioned at (0, 8.0), and a 1.0-kg mass is positioned at (12, 0). What are the coordinates of a 4.0-kg mass which will result in the center of mass of the system of three masses being located at the origin, (0, 0)? A) (-3.0, -6.0) B) (-12, -8.0) C) (3.0, 6.0) D) (-6.0, -3.0)

A

A 3.0-kg object moves to the right with a speed of 2.0 m/s. It collides in a perfectly elastic collision with a 6.0-kg object moving to the left at 1.0 m/s. What is the total kinetic energy after the collision? A) 9.0 J B) 6.0 J C) 3.0 J D) 0 J

A

A 70-kg astronaut is space-walking outside the space capsule and is stationary when the tether line breaks. As a means of returning to the capsule he throws his 2.0-kg space hammer at a speed of 14 m/s away from the capsule. At what speed does the astronaut move toward the capsule? A) 0.40 m/s B) 1.5 m/s C) 3.5 m/s D) 5.0 m/s

A

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) Neither; both experienced the same magnitude impulse. B) the Ping-Pong ball C) the bowling ball D) It's impossible to tell since the velocities after the collision are unknown.

A

A ball of mass 0.10 kg is dropped from a height of 12 m. Its momentum when it strikes the ground is A) 1.5 kgoem/s. B) 1.8 kgoem/s. C) 2.4 kgoem/s. D) 4.8 kgoem/s.

A

A constant 9.0-N net force acts for 2.0 s on a 6.0-kg object. What is the object's change of velocity? A) 3.0 m/s B) 9.0 m/s C) 27 m/s D) 110 m/s

A

A golf ball traveling 3.0 m/s to the right collides in a head-on collision with a stationary bowling ball in a friction-free environment. If the collision is almost perfectly elastic, the speed of the golf ball immediately after the collision is A) slightly less than 3.0 m/s. B) slightly greater than 3.0 m/s. C) equal to 3.0 m/s. D) much less than 3.0 m/s.

A

A railroad freight car, mass 15,000 kg, is allowed to coast along a level track at a speed of 2.0 m/s. It collides and couples with a 50,000-kg second car, initially at rest and with brakes released. What is the speed of the two cars after coupling? A) 0.46 m/s B) 0.60 m/s C) 1.2 m/s D) 1.8 m/s

A

A rubber ball and a lump of putty have equal mass. They are thrown with equal speed against a wall. The ball bounces back with nearly the same speed with which it hit. The putty sticks to the wall. Which objects experiences the greater momentum change? A) the ball B) the putty C) Both experience the same momentum change. D) cannot be determined from the information given

A

A sailboat of mass m is moving with a momentum p. How would you represent its kinetic energy in terms of these two quantities? A) p2/(2m) B) 1/2 mp2 C) mp D) mp/2

A

A small object with momentum 5.0 kgoem/s approaches head-on a large object at rest. The small object bounces straight back with a momentum of magnitude 4.0 kgoem/s. What is the magnitude of the large object's momentum change? A) 9.0 kgoem/s B) 5.0 kgoem/s C) 4.0 kgoem/s D) 1.0 kgoem/s

A

In a game of pool, the white cue ball hits the #5 ball and stops, while the #5 ball moves away with the same velocity as the cue ball had originally. The type of collision is A) elastic. B) inelastic. C) completely inelastic. D) any of the above, depending on the mass of the balls.

A

In an elastic collision, if the momentum is conserved, then which of the following statements is true about kinetic energy? A) Kinetic energy is also conserved. B) Kinetic energy is gained. C) Kinetic energy is lost. D) none of the above

A

The area under the curve on a Force versus time (F vs. t) graph represents A) impulse. B) momentum. C) work. D) kinetic energy.

A

Two cars collide head-on on a level friction-free road. The collision was completely inelastic and both cars quickly came to rest during the collision. What is true about the velocity of this system's center of mass? A) It was always zero. B) It was never zero. C) It was not zero, but ended up zero. D) none of the above

A

Two objects collide and bounce off each other. Linear momentum A) is definitely conserved. B) is definitely not conserved. C) is conserved only if the collision is elastic. D) is conserved only if the environment is frictionless.

A

When is kinetic energy conserved? A) in elastic collisions B) in inelastic collisions C) in any collision in which the objects do not stick together D) in all collisions

A

A very heavy object moving with speed v collides head-on with a very light object at rest. The collision is elastic, and there is no friction. The heavy object barely slows down. What is the speed of the light object after the collision? A) nearly v B) nearly 2v C) nearly 3v D) nearly infinite

B

If you pitch a baseball with twice the kinetic energy you gave it in the previous pitch, the magnitude of its momentum is A) the same. B) 1.41 times as much. C) doubled. D) 4 times as much.

B

In a game of pool, the white cue ball hits the #9 ball and is deflected at a 35e angle to the original line of motion. What is the angle of deflection below the original line of motion for the #9 ball? A) 35e B) 55e C) 75e D) 90e

B

The center of mass of a two-particle system is at the origin. One particle is located at (3.0 m, 0) and has a mass of 2.0 kg. What is the location of the second mass of 3.0 kg? A) (-3.0 m, 0) B) (-2.0 m, 0) C) (2.0 m, 0) D) (3.0 m, 0)

B

Three masses are positioned as follows: 2.0 kg at (0, 0), 2.0 kg at (2.0, 0), and 4.0 kg at (2.0, 1.0). Determine the coordinates of the center of mass. A) (0.50, 1.5) B) (1.5, 0.50) C) (2.5, 1.5) D) (2.5, 0.50)

B

Three masses, 1.0 kg, 2.0 kg, and 3.0 kg, are located at (0, 0), (1.0 m, 1.0 m), and (2.0 m, -2.0 m), respectively. What is the location of the center of mass of the system? A) (1.3 m, 0.67 m) B) (1.3 m, -0.67 m) C) (-1.3 m, 0.67 m) D) (-1.3 m, -0.67 m)

B

Two identical 1500-kg cars are moving perpendicular to each other. One moves with a speed of 25 m/s due north and the other moves at 15 m/s due east. What is the total momentum of the system? A) 4.4 ˛ 104 kgoem/s at 31e N of E B) 4.4 ˛ 104 kgoem/s at 59e N of E C) 6.0 ˛ 104 kgoem/s at 31e N of E D) 6.0 ˛ 104 kgoem/s at 59e N of E

B

Two objects collide and stick together. Kinetic energy A) is definitely conserved. B) is definitely not conserved. C) is conserved only if the collision is elastic. D) is conserved only if the environment is frictionless.

B

Two objects move on a level frictionless surface. Object A moves east with a momentum of 24 kgoem/s. Object B moves north with momentum 10 kgoem/s. They make a perfectly inelastic collision. What is the magnitude of their combined momentum after the collision? A) 14 kgoem/s B) 26 kgoem/s C) 34 kgoem/s D) cannot be determined without knowing masses and velocities

B

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 cannonball and cannon is conserved. C) energy of the cannon is greater than the energy of the cannonball. D) momentum of the cannon is greater than the energy of the cannonball.

B

You (50-kg mass) skate on ice at 4.0 m/s to greet your friend (40-kg mass), who is standing still, with open arms. As you collide, while holding each other, with what speed do you both move off together? A) zero B) 2.2 m/s C) 5.0 m/s D) 23 m/s

B

A 0.10-kg object with a velocity of 0.20 m/s in the +x direction makes a head-on elastic collision with a 0.15 kg object initially at rest. What is the final velocity of the 0.10-kg object after collision? A) -0.16 m/s B) +0.16 m/s C) -0.040 m/s D) +0.040 m/s

C

A 1500-kg car traveling at 90.0 km/h east collides with a 3000-kg car traveling at 60.0 km/h south. The two cars stick together after the collision. (See Fig. 7-1.) What is the direction of motion of the cars after collision? A) 36.9e S of E B) 36.9e E of S C) 53.1e S of E D) 53.1e E of S

C

A 2.0-kg mass moves with a speed of 5.0 m/s. It collides head-on with a 3.0 kg mass at rest. If the collision is perfectly inelastic, what is the speed of the masses after the collision? A) 10 m/s B) 2.5 m/s C) 2.0 m/s D) 0, since the collision is inelastic

C

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

C

A 3.0-kg object moves to the right at 4.0 m/s. It collides head-on with a 6.0-kg object moving to the left at 2.0 m/s. Which statement is correct? A) The total momentum both before and after the collision is 24 kgoe m/s. B) The total momentum before the collision is 24 kgoem/s, and after the collision is 0 kgoem/s. C) The total momentum both before and after the collision is zero. D) None of the above is true.

C

A fire hose is turned on the door of a burning building in order to knock the door down. This requires a force of 1000 N. If the hose delivers 40 kg per second, what is the minimum velocity of the stream needed, assuming the water doesn't bounce back? A) 15 m/s B) 20 m/s C) 25 m/s D) 30 m/s

C

A freight car moves along a frictionless level railroad track at constant speed. The car is open on top. A large load of coal is suddenly dumped into the car. What happens to the velocity of the car? A) It increases. B) It remains the same. C) It decreases. D) cannot be determined from the information given

C

A handball of mass 0.10 kg, traveling horizontally at 30 m/s, strikes a wall and rebounds at 24 m/s. What is the change in the momentum of the ball? A) 0.60 kgoem/s B) 1.2 kgoem/s C) 5.4 kgoem/s D) 72 kgoem/s

C

A railroad car, of mass 200 kg, rolls with negligible friction on a horizontal track with a speed of 10 m/s. A 70-kg stunt man drops straight down a distance of 4.0 m, and lands in the car. How fast will the car be moving after this happens? A) 2.8 m/s B) 4.7 m/s C) 7.4 m/s D) 10 m/s

C

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 truck experiences the greater average force. B) The small car experiences the greater average force. C) The small car and the truck experience the same average force. D) It is impossible to tell since the masses and velocities are not given.

C

A small object collides with a large object and sticks. Which object experiences the larger magnitude of momentum change? A) the large object B) the small object C) Both objects experience the same magnitude of momentum change. D) cannot be determined from the information given

C

A toy rocket, of mass 0.12 kg, achieves a velocity of 40 m/s after 3.0 s, when fired straight up. What average thrust force does the rocket engine exert? A) 1.2 N B) 1.6 N C) 2.8 N D) 4.4 N

C

In an inelastic collision, if the momentum is conserved, then which of the following statements is true about kinetic energy? A) Kinetic energy is also conserved. B) Kinetic energy is gained. C) Kinetic energy is lost. D) none of the above

C

Tightrope walkers walk with a long flexible rod in order to A) increase their total weight. B) allow both hands to hold onto something. C) lower their center of mass. D) move faster along the rope.

C

Two astronauts, of masses 60 kg and 80 kg, are initially at rest in outer space. They push each other apart. What is their separation after the lighter astronaut has moved 12 m? A) 15 m B) 18 m C) 21 m D) 24 m

C

Use Table 7-1 to calculate the position of the CM of a whole leg including the foot when the leg is stretched straight out. Assume the person is 1.60 m tall. A) 0.20 m above the bottom of the foot B) 0.32 m above the bottom of the foot C) 0.51 m above the bottom of the foot D) 0.54 m above the bottom of the foot

C

What is the SI unit of momentum? A) Noem B) N/s C) Noes D) N/m

C

What is the momentum of a 2000-kg truck traveling at 35 m/s? A) 57 kgoem/s B) 3.5 ˛ 104 kgoem/s C) 7.0 ˛ 104 kgoem/s D) 7.0 ˛ 105 kgoem/s

C

When a light beach ball rolling with a speed of 6.0 m/s collides with a heavy exercise ball at rest, the beach ball's speed after the collision will be, approximately, A) 0. B) 3.0 m/s. C) 6.0 m/s. D) 12 m/s.

C

Which of the following is a false statement? A) For a uniform symmetric object, the center of mass is at the center of symmetry. B) For an object on the surface of the Earth, the center of gravity and the center of mass are the same point. C) The center of mass of an object must lie within the object. D) The center of gravity of an object may be thought of as the "balance point."

C

Which of the following is an accurate statement? A) The momentum of a projectile is constant. B) The momentum of a moving object is constant. C) If an object is acted on by a non-zero net external force, its momentum will not remain constant. D) If the kinetic energy of an object is doubled, its momentum will also double.

C

A 0.060-kg tennis ball, initially moving at a speed of 12 m/s, is struck by a racket causing it to rebound in the opposite direction at a speed of 18 m/s. What is the change in momentum of the ball? A) 0.36 kgoem/s B) 0.72 kgoem/s C) 1.1 kgoem/s D) 1.8 kgoem/s

D

A 0.10-kg ball is dropped onto a table top. The speeds of the ball right before and right after hitting the table top are 5.0 m/s and 4.0 m/s, respectively. If the collision between the ball and the table top lasts 0.15 s, what is the magnitude of the average force exerted on the ball by the table top? A) 0.67 N B) 1.3 N C) 3.0 N D) 6.0 N

D

A 1200-kg ferryboat is moving south at 20 m/s. What is the magnitude of its momentum? A) 1.7 ˛ 10-3 kgoem/s B) 6.0 ˛ 102 kgoem/s C) 2.4 ˛ 103 kgoem/s D) 2.4 ˛ 104 kgoem/s

D

A 2.0-kg softball is pitched to you at 20 m/s. You hit the ball back along the same path, and at the same speed. If the bat was in contact with the ball for 0.10 s, what is the magnitude of the average force the bat exerted? A) zero B) 40 N C) 400 N D) 800 N

D

A 3.0-kg object moves to the right at 4.0 m/s. It collides in a perfectly inelastic collision with a 6.0 kg object moving to the left at 2.0 m/s. What is the total kinetic energy after the collision? A) 72 J B) 36 J C) 24 J D) 0 J

D

A 4.0-N force acts for 3.0 s on an object. The force suddenly increases to 15 N and acts for one more second. What impulse was imparted by these forces to the object? A) 12 Noes B) 15 Noes C) 19 Noes D) 27 Noes

D

A 4.00-kg mass sits at the origin, and a 10.0-kg mass sits at x = + 21.0 m. Where is the center of mass on the x-axis? A) +7.00 m B) +10.5 m C) +14.0 m D) +15.0 m

D

A car of mass m, traveling with a velocity v, strikes a parked station wagon, who's 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) 1/3 C) 1/4 D) 2/3

D

A plane, flying horizontally, releases a bomb, which explodes before hitting the ground. Neglecting air resistance, the center of mass of the bomb fragments, just after the explosion A) is zero. B) moves horizontally. C) moves vertically. D) moves along a parabolic path.

D

A rubber ball with a speed of 5.0 m/s collides head-on elastically with an identical ball at rest. What is the speed of the initially stopped ball after the collision? A) zero B) 1.0 m/s C) 2.5 m/s D) 5.0 m/s

D

A very light object moving with speed v collides head-on with a very heavy object at rest, in a frictionless environment. The collision is almost perfectly elastic. The speed of the heavy object after the collision is A) slightly greater than v. B) equal to v. C) slightly less than v. D) much less than v.

D

Consider two unequal masses, M and m. Which of the following statements is false? A) The center of mass lies on the line joining the centers of each mass. B) The center of mass is closer to the larger mass. C) It is possible for the center of mass to lie within one of the objects. D) If a uniform rod of mass m were to join the two masses, this would not alter the position of the center of mass of the system without the rod present.

D

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

D

State Newton's second law for a system of particles.

The sum of all forces acting on the system is equal to the total mass of the system times the acceleration of its center of mass.

State the law of conservation of momentum.

The total momentum of an isolated system of objects remains constant.

A 100-kg football linebacker moving at 2.0 m/s tackles head-on an 80-kg halfback running 3.0 m/s. Neglecting the effects due to digging in of cleats, A) the linebacker will drive the halfback backward. B) the halfback will drive the linebacker backward. C) neither player will drive the other backward. D) this is a simple example of an elastic collision.

B

A 1000-kg car traveling at 25 m/s runs into the rear of a stopped car that has a mass of 1500 kg and they stick together. What is the speed of the cars after the collision? A) 5.0 m/s B) 10 m/s C) 15 m/s D) 20 m/s

B

A 1500-kg car traveling at 90.0 km/h east collides with a 3000-kg car traveling at 60.0 km/h south. The two cars stick together after the collision. (See Fig. 7-1.) What is the speed of the cars after collision? A) 8.33 m/s B) 13.9 m/s C) 17.4 m/s D) 21.7 m/s

B

A 2000-kg car, traveling to the right at 30 m/s, collides with a brick wall and comes to rest in 0.20 s. What is the average force the car exerts on the wall? A) 12,000 N to the right B) 300,000 N to the right C) 60,000 N to the right D) none of the above

B

A 50-kg pitching machine (excluding the baseball) is placed on a frozen pond. The machine fires a 0.40-kg baseball with a speed of 35 m/s in the horizontal direction. What is the recoil speed of the pitching machine? (Assume negligible friction.) A) 0.14 m/s B) 0.28 m/s C) 0.70 m/s D) 4.4 ˛ 103 m/s

B

A car of mass 1000 kg moves to the right along a level, straight road at a speed of 6.0 m/s. It collides directly with a stopped motorcycle of mass 200 kg. What is the total momentum after the collision? A) zero B) 6000 kgoem/s to the right C) 2000 kgoem/s to the right D) 10,000 kgoem/s to the right

B

A child falls sideways off a sled while sledding on frictionless ice. What happens to the velocity of the sled? A) It increases. B) It remains the same. C) It decreases. D) cannot be determined from the information given

B

A machine gun, of mass 35.0 kg, fires 50.0-gram bullets, with a muzzle velocity of 750 m/s, at the rate of 300 rounds per minute. What is the average force exerted on the machine gun mount? A) 94.0 N B) 188 N C) 219 N D) 438 N

B

A red ball with a velocity of +3.0 m/s collides head-on with a yellow ball of equal mass moving with a velocity of -2.0 m/s. What is the velocity of the yellow ball after the collision? A) zero B) +3.0 m/s C) -2.0 m/s D) +5.0 m/s

B

A small bomb, of mass 10 kg, is moving toward the North with a velocity of 4.0 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) zero B) 40 m/s north C) 40 m/s south D) none of the above

B

State Newton's second law in terms of momentum.

The rate of change of momentum of an object is equal to the net force applied to it.