Physics for Elementary Teachers Exam 1
A horse is hitched to a buggy. The horse exerts a force of 600 N forward on its harness, and the harness exerts a force of 600 N backward on the horse. Are these two forces an action/reaction pair? a) Yes. b) No. c) It cannot be determined without knowing if the buggy is moving or stationary.
A
A car is in uniform circular motion on a circular track. As calculated from an axis through the center of the circle, the torque on the car is zero. a) True b) False
A
A car is in uniform circular motion on a circular track. As calculated from an axis through the center of the circle, the car's angular momentum is constant. a) True b) False
A
A car is in uniform circular motion on a circular track. As calculated from an axis through the center of the circle, the car's moment of inertia is constant. a) True b) False
A
A student places a textbook on a table. The table "knows" how much force to exert on the textbook because a) the table deforms until it pushes back on the book with the force required to keep the book from coming through the table b) the table reflects the force like a mirror reflects light c) the table blocks the force of gravity from objects in contact with its upper surface
A
10.2 cm = ___ m a)0.102 b)1.02 c)102 d)0.0102
A
0.75 m = ___ cm a)75 b)750 c)7.5 d)7500
A
Action at a distance, such as is the case for gravity, was once thought to be illogical and therefore untrue. Why was this action ultimately accepted? a) It was accepted because it does the best job of explaining the results of observation and experiment. b) It was accepted because Newton had powerful political friends. c) It was accepted because of the discovery of quantum entanglement. d) It was accepted because of the discovery of the ether that carries light waves.
A
During typical highway driving, power of a car's engine is mostly used to ____. a) overcome air drag b) overcome static friction between the tires and the road c) overcome kinetic friction between the tires and the road d) increase the gravitational potential energy e) increase the kinetic energy
A
In order for a normal force to exist, ____. a) the object must be in contact with a surface b) gravity must be present c) friction must be present d) all of the above e) a) and b)
A
Kepler's First Law of Planetary Motion ("Planets move along ellipses, with the sun at one focus.") is a consequence of ___. a) an advanced calculation involving Newton's Law of Universal Gravitation b) the conservation of angular momentum c) centripetal force arising from Newton's Law of Universal Gravitation
A
Which of the following is a good analogy for Newton's Third Law? a) Veronica gives Betty $10. As a result of the transaction, Veronica is $10 poorer and Betty is $10 richer. b) Joe Frazier hits Muhammad Ali. A few seconds later, Muhammad Ali hits Joe Frazier. c) Zeke borrows $100,000 for his business. After doing business for a year, he is able to pay off the debt and keep a profit. d) By going into business together, Ben and Jerry do better than either would separately. e) Two friends are playing roulette in Vegas. On one spin, the ball lands in pocket #11. One friend had bet $20 that the ball would land in an even-numbered pocket and loses his bet, but the other had bet $20 that the ball would land in the first dozen pockets and wins an additional $40.
A
Which of the following is an accurate statement about an object moving in one dimension? a) If the velocity and acceleration have opposite signs, the object is slowing down. b) If position and velocity have opposite signs, the object is slowing down. c) If the object is not moving, it must have zero acceleration at that instant. d) It is not possible for an object to have both negative velocity and negative acceleration.
A
Which of the following is not a conservative force? a) Wind resistance b) Gravity c) Spring force d) Electrostatic force
A
While reducing the mass of a racing bike, the greatest benefit is realized from reducing the mass of the tires and wheel rims. What is the most important reason this allows a racer to achieve greater accelerations than would an identical reduction in the mass of the bicycle's frame? a) The wheels have both translational and rotational kinetic energy, both of which are proportional to the wheels' mass. b) Reducing the mass of the wheels decreases their wind resistance. c) Racing frames have already been engineered to a bare minimum, but it has been considered unsafe to make much change in wheels due to the large forces they encounter. d) Reducing the mass of the wheel reduces the component of the centripetal force that must be supplied by the normal force from the road, which reduces the rolling friction.
A
A 70-kg wide receiver running west at 8 m/s collides head on with, and is seized by, a 140-kg lineman lumbering eastward at 4 m/s. In this collision, the greater change in kinetic energy is experienced by the a) ★wide receiver b) lineman c) neither; they both experience the same change in kinetic energy d) the changes in kinetic energy are equal in magnitude but opposite in direction
A, Even though momentum is conserved, the bigger change in energy goes into the smaller object. This is one of the main reasons it is better to experience the "kick" from a rifle than to be hit by the bullet.
Which ball eventually strikes the ground with the greatest speed? a) Both strike the ground with the same speed. b) The red ball strikes the ground with the greatest speed. c) The blue ball strikes the ground with the greatest speed. d) The ball with the largest weight strikes the ground with the greatest speed. e) The ball with the smallest weight strikes the ground with the greatest speed.
A, One way to see this is from conservation of energy.
1.2 kg = ___ grams a)120 b)1200 c)12000 d)0.12
B
11. 593 grams = ____ kg a)5.93 b)0.593 c)0.0593 d)59.3
B
A car is in uniform circular motion on a circular track. As calculated from an axis outside the circle, the car's linear momentum is constant. a) True b) False
B
A car is in uniform circular motion on a circular track. As calculated from an axis outside the circle, the torque on the car is zero. a) True b) False
B
A car is in uniform circular motion on a circular track. As calculated from an axis outside the circle, the car's angular momentum is constant. a) True b) False
B
A car is in uniform circular motion on a circular track. As calculated from an axis outside the circle, the car's moment of inertia is constant. a) True b) False
B
A car is in uniform circular motion on a circular track. As calculated from an axis through the center of the circle, the car's linear momentum is constant. a) True b) False
B
A conservative force is ___. a) any force in the same direction as the velocity b) a force for which the work done around any closed path is zero c) a force that does no work d) a force that is directly proportional to the velocity
B
A spark of static electricity, such as that you might receive from a doorknob on a cold dry day, may carry a few hundred watts of power. Why are you not injured by such a spark? a) Rubber-soled shoes keep you safe from electricity. b) Although the power is high, the spark only lasts for a tiny fraction of a second, so it contains very little energy. c) Dry human skin has a very high electrical resistance. d) Because electricity has almost no mass, it has a small momentum and so cannot hurt you.
B
An experiment uses a fan cart to study motion with constant acceleration. In one run, velocity vs. time graph II is produced. Assume this graph is all you know about the cart's motion! What is the acceleration of the cart at time zero? a) 0 cm/s2 b) 20 cm/s2 c) 40 cm/s2 d) 120 cm/s2 e) The answer cannot be determined solely from the information on the v vs. t graph.
B
Angular momentum is conserved only in objects moving along circular paths. a) True b) False
B
Consider two frictionless inclined planes with the same vertical height. Plane 1 makes an angle of 25o with the horizontal, and plane 2 makes an angle of 75o with the horizontal. Mass m1 is placed at the top of plane 1, and mass m2 is placed at the top of plane 2. Both masses are released at the same time and slide down the plane. At the bottom, which mass has a higher speed? a) It cannot be determined without knowing the values of the masses. b) Both masses have the same speed. c) m2 d) m1
B
Every force has a corresponding potential energy. a) True b) False
B
In an inelastic collision ____________. a) mechanical energy is conserved b) momentum is conserved c) both mechanical energy and momentum are conserved
B
Kepler's Second Law of Planetary Motion ("A line from the planet to the sun sweeps out equal areas over equal periods of time.") is a consequence of ___. a) an advanced calculation involving Newton's Law of Universal Gravitation b) the conservation of angular momentum c) centripetal force arising from Newton's Law of Universal Gravitation
B
Todd uses a block and tackle to lift a heavy box 3 m, doing 500 J of work against gravity in the process. a) As a result, the gravitational potential energy is now 500 J. b) As a result, the gravitational potential energy has increased by 500 J. c) As a result, the gravitational potential energy is now -500 J. d) As a result, the gravitational potential energy has decreased by 500 J. e) There is no gravitational energy associated with friction.
B
When a ball at rest hangs by a single vertical string, tension in the string is mg. If the ball is made to move in a horizontal circle so that the string describes a cone, string tension a) is equal to mg, always. b) is greater than mg, always. c) is less than mg, always. d) may be greater or less than mg depending on the speed of the ball.
B
When you learn to drive, you discover that you need to let up slightly on the brake pedal as you come to a stop or the car will stop with a jerk. Why does this happen? a) As the car comes to a stop, it is acted upon by static and kinetic friction simultaneously. b) As the car comes to a stop, the kinetic friction between the brake pads and the disks suddenly transitions to static friction, which is stronger for the same normal force. c) As the car comes to a stop, the kinetic friction between the tires and the asphalt suddenly transitions to static friction, which is stronger for the same normal force. d) As the car comes to a stop, the friction between the brake pads alternates rapidly between static and kinetic friction, the same slip-grab process that sometimes makes chalk screech as it is drawn across the chalkboard.
B
Which of the following has a mass of about 1 kg? a) a gallon of milk c) a marshmallow e) a loaf of bread b) a quart of milk d) a stick of butter
B
You wish to calculate the consequences of the conservation of angular momentum on the collision of two extended objects. The angular momentum of each of the objects should be calculated about its center of mass. a) True b) False
B
Felix Baumgartner is performing a practice skydive. Having jumped from a height of 10 km, he soon attains a terminal velocity of -54 m/s (up is the positive direction). The net force acting on Baumgartner is a) is positive b) is zero c) is negative d) cannot be determined, even in sign, from the information given
B, His velocity is unchanged, so his acceleration is zero, and force = mass × acceleration.
Tommy throws a red ball straight up into the air at an initial speed of 15 m/s from an initial height of 1.5 m. At the same time, Michael throws a blue ball straight down at an initial speed of 15 m/s from an initial height of 1.5 m. Ignore wind resistance. USE FOR 20-24 At the instant when the red ball reaches its maximum height, its acceleration is ___. a) zero b) the same as at any other time c) larger than at any other time d) smaller than at any other time, but not zero
B, The ball's acceleration will be 9.8 m/s2 straight down, due to gravity.
A box in a secret warehouse contains the most recent legendary find of a colorful archaeologist. The box experiences a gravitational force of 2000 N down and a support force of 2000 N up. Are these two forces an action/reaction pair? a) Yes. b) No. c) It cannot be determined without knowing if the box is moving or stationary.
B, The force of the box on the floor is in an action/reaction pair with the force of the floor on the box, but the gravitational force of the earth on the box is not - even though it has the same value in this case. The fact that they have the same value can be seen as a coincidence, though a common coincidence. After all, the box could be partially supported by a balloon, in which case the floor would only push up with the force necessary to keep the box from crashing through the floor.
Answer the next 2 questions for projectile motion on level ground assuming negligible air resistance (the initial angle being neither 0o nor 90o ). Is the velocity ever zero? a) Yes, at the peak of the trajectory. b) No, never; the magnitude of the velocity vector changes, but it is never zero. c) No, never; the direction of the velocity changes, but its magnitude remains constant. d) Yes, when the projectile hits the ground.
B, The projectile's vertical motion slows on the way up, is briefly zero at the top of its trajectory, and then speeds up again on the way down. Its horizontal component of velocity does not change, though, so the velocity vector (both components together) is never zero.
A 70-kg wide receiver running west at 8 m/s collides head on with, and is seized by, a 140-kg lineman lumbering eastward at 4 m/s. In this collision, the greater change in momentum is experienced by the a) wide receiver b) lineman c) neither; they both experience the same change in momentum d) the changes in momentum are equal in magnitude but opposite in direction
D
A bullet is shot out of a precisely horizontal rifle at 1000 m/s over flat ground. An identical bullet is simply dropped from the same height as the rifle. Which bullet hits the ground first? a) The bullet fired from the gun hits the ground first. b) The bullet that was only dropped hits the ground first. c) Both bullets hit the ground at the same time.
C
An experiment uses a fan cart to study motion with constant acceleration. In one run, velocity vs. time graph II is produced. Assume this graph is all you know about the cart's motion! What is the velocity of the cart at time zero? a) 0 cm/s b) 20 cm/s c) 40 cm/s d) 120 cm/s e) The answer cannot be determined solely from the information on the v vs. t graph.
C
Consider a ball of mass m rolling in a horizontal circular path on the inside surface of a cone (like a marble rolling inside a funnel). The only forces acting on the ball are the normal force and gravity. The normal force on the ball a) is equal to mg, always. c) is greater than mg, always. b) may be greater or less than mg. d) is less than mg, always.
C
Felix Baumgartner is performing a practice skydive. Having jumped from a height of 10 km, he soon attains a terminal velocity of -54 m/s (up is the positive direction). Baumgartner's momentum is a) is positive b) is zero c) is negative d) cannot be determined, even in sign, from the information given
C
Gravitational potential energy is defined ____. a) near the surface of the earth, but not in astronomical situations b) in astronomical situations, but not near the surface of the earth c) both near the surface of the earth and in astronomical situations d) neither near the surface of the earth nor in astronomical situations
C
Hooke's Law is ___. a) always rigorously true - that's why it's called a law b) true as long as the effects of quantum mechanics and relativity are ignored c) a robust approximation that is justified in many circumstances and mathematically convenient d) obsolete, having been replaced by Newton's Theory of Universal Gravitation e) an alternative way of looking at the centripetal force
C
How are instantaneous velocity and instantaneous speed related to one another? How do they differ? a) Instantaneous velocity and instantaneous speed are the same except that instantaneous velocity can be negative. b) Velocity is just the word physicists use for speed. c) Instantaneous speed is the magnitude of the instantaneous velocity, but instantaneous velocity also includes the direction. d) Instantaneous velocity and instantaneous speed are the same in one dimension, but different in two or three dimensions.
C
In an elastic collision, ___. a) mechanical energy is conserved b) momentum is conserved c) both mechanical energy and momentum are conserved
C
In an inelastic collision ______. a) mechanical energy is always conserved b) mechanical energy always increases c) mechanical energy always decreases d) mechanical energy may increase, decrease, or remain the same
C
Kepler's Third Law of Planetary Motion ("A planet's 'year' is proportional to its average radius to the power 3/2.") is a consequence of ___. a) an advanced calculation involving Newton's Law of Universal Gravitation b) the conservation of angular momentum c) centripetal force arising from Newton's Law of Universal Gravitation
C
The space shuttle had a mass of about 2.03 × 106 kg. Suppose it was at rest (relative to the International Space Station). It then fired its thrusters, expelling 4.567 × 103 kg of exhaust and acquiring a velocity of 10 m/s relative to the ISS. Which of the following is true? a) The exhaust and the shuttle had equal momentum and equal kinetic energy. b) The exhaust and the shuttle had equal momentum, but the shuttle had more kinetic energy. c) The exhaust and the shuttle had equal momentum, but the exhaust had more kinetic energy. d) The exhaust and the shuttle had equal kinetic energy, but the shuttle had more momentum. e) The exhaust and the shuttle had equal kinetic energy, but the exhaust had more momentum.
C
When you launch a marble off a table at an angle (like you did in the PHY 202 lab) at a fixed speed, the angle with the horizon which will cause the marble to go the longest distance before hitting the ground is ___. a) greater than 45 degrees b) equal to 45 degrees c) less than 45 degrees d) either of two angles, one larger than 45 degrees and one smaller than 45 degrees
C
Which of the following is the best example of an inelastic collision? a) A basketball bounces off the backboard. b) Pellets of birdshot lose velocity as they break a clay pigeon. c) A rifle bullet is stopped by and contained within a stump. d) A space probe gets a gravitational slingshot from Jupiter en route to Saturn. e) A swordsman slices through a watermelon.
C
A ball thrown horizontally from the top of a building hits the ground in 0.50 s. If it had been thrown with twice the speed in the same direction, it would have hit the ground in a) 4.0 s b) 1.0 s c) 0.50 s d) 0.25 s e) 0.125 s
C, How long the ball is in the air is a question about the ball's vertical motion. The horizontal component of its velocity has nothing to do with that.
A fireworks shell explodes, breaking into many small cinders. Realistically, how is the motion of the center of mass affected by the explosion? a) It continues to move along a parabola. b) It immediately comes to a stop and immediately begins to fall. c) It immediately comes to a stop, and only begins to fall after a second or so after the cinders burn out. d) Wind resistance will slow both its horizontal and vertical velocity and will cause it to accelerate more slowly toward the ground.
D
A math book and a physics book are tied together with a length of string. With the string taut, the physics book, which is slightly more massive than the math book, is pushed off the edge of a table. As the physics book falls, the math book is dragged horizontally across the table surface. With no friction, acceleration of the two books is a) zero. d) a value between zero and g. b) g/2. e) a value that could be greater than g c) g.
D
An offensive lineman for the Herd reasons that it is senseless to try to out-push the opposing player, since no matter how hard he pushes he will experience an equal and opposite force from the other player. a) The lineman is correct, but only if he holds onto the opposing player so that they have the same acceleration. b) The lineman is wrong, because Newton's Laws apply only to inanimate objects. c) The lineman is wrong, because as the football players push against each other they inevitably rotate, and Newton's Laws do not apply in rotating frames of reference. d) The lineman is wrong, because he is not taking into account other forces (the action of his feet on the earth and vice versa and also the action of his opponent's feet on the earth and vice versa).
D
Can the kinetic energy for a system of two colliding objects be conserved in the x-direction while not being conserved in the y-direction? a) No; either kinetic energy is conserved or it is not. b) Yes, but only if the kinetic energy in the x-direction is zero. c) Yes, but only if the kinetic energy in the y-direction is zero. d) No, because kinetic energy is a scalar quantity, not a vector. e) Yes, if the total external force acts on the system only in the y-direction.
D
The New Horizons probe has passed Pluto and is moving at 16.26 km/s away from the earth. Which of the following is true? a) If it wishes to maintain its current velocity, it must fire its rockets. b) Firing its rockets will have no effect, because there is no air for them to push against. c) Its direction can be changed only by gravity. d) No action is necessary to maintain its current velocity.
D
The conservation of energy is important because ____. a) it reveals an important basic principle about the universe b) it allows us to use scalars to solve certain problems that would otherwise require vectors c) it allows us to solve problems using algebra that would otherwise require calculus d) all of the above
D
The tension in a string is a force directed a) up b) in the opposite direction to the normal force c) perpendicular to the string d) parallel to the string
D
When is the magnitude of the velocity vector a maximum? a) At the peak of the trajectory. b) At the instant after the object is launched, and only then. c) At the instant before the object lands, and only then. d) At the instant after the object is launched and again at the instant before it lands. e) The velocity has a constant magnitude; only the direction changes.
D
Which of the following is the best example of an elastic collision? a) A basketball bounces off the backboard. b) Pellets of birdshot lose velocity break a clay pigeon. c) A rifle bullet is stopped by and contained within a stump. d) A space probe gets a gravitational slingshot from Jupiter en route to Saturn. e) A swordsman slices through a watermelon.
D
An experiment uses a fan cart to study motion with constant acceleration. In one run, velocity vs. time graph II is produced. Assume this graph is all you know about the cart's motion! What is the position of the cart at time zero? a) 0 cm b) 20 cm c) 40 cm d) 120 cm e) The answer cannot be determined solely from the information on the v vs. t graph.
E
Can the momentum for a system of two colliding objects be conserved in the x-direction while not being conserved in the y-direction? a) No; either momentum is conserved or it is not. b) Yes, but only if the momentum in the x-direction is zero. c) Yes, but only if the momentum in the y-direction is zero. d) No, because momentum is a scalar quantity, not a vector. e) Yes, if the total external force acts on the system only in the y-direction.
E
Define and describe centripetal force. a) Centripetal force is the force that pushes an object in circular motion outward from the center of the circle. It can be provided by any one force. b) Centripetal force is the force that pushes an object in circular motion outward from the center of the circle. It can be provided by any combination of forces or components of forces. c) Centripetal force is the force necessary to bend an object's path out of straight-line motion. It can be provided by any one force. d) Centripetal force is the force necessary to bend an object's path out of straight-line motion. It can be provided by any one force or a component of any one force. e) Centripetal force is the force necessary to bend an object's path out of straight-line motion. It can be provided by any combination of forces or components of a forces.
E
Few collisions involve an increase in mechanical energy, because this would ___. a) violate the law of the conservation of energy b) require the conversion of mass into energy c) require a velocity that is an imaginary number d) require relativistic velocity e) indicate an unstable initial condition
E
Todd pushes a heavy box 10 m down the hallway, doing 500 J of work against friction in the process. a) As a result, the friction potential energy is now 500 J. b) As a result, the friction potential energy has increased by 500 J. c) As a result, the friction potential energy is now -500 J. d) As a result, the friction potential energy has decreased by 500 J. e) There is no potential energy associated with friction.
E
At the instant the balls leave the boys' hands, which one has the largest acceleration? a) The red ball has the largest acceleration. b) The blue ball has the largest acceleration. c) The ball with the largest weight has the largest acceleration. d) The ball with the smallest weight has the largest acceleration e) Both have the same acceleration.
E, Again, it is 9.8 m/s2 straight down, due to gravity.
The kinetic energy can never be negative, and it is zero only when the velocity is zero. This fact can be used to identify the inertial reference frame that is preferred by nature. TRUE OR FALSE
FALSE
In physics, which of the following are necessary for a "collision" to take place? I) There is an exchange of momentum between two objects. II) The total mechanical energy is conserved. III) The objects "trade paint", meaning they touch each other. IV) The interaction between the objects takes place only for a limited time.
I & IV
An experiment uses a fan cart to study motion with constant acceleration. In one run, position vs. time graph V is produced. Which velocity vs. time graph is produced by this run?
I, The slope of the position vs time graph starts out horizontal, so the initial velocity must be zero. The position vs. time graph curves downward like a frown, so the acceleration is negative, meaning the slope of the velocity vs. time graph must be downward.
An experiment uses a fan cart to study motion with constant acceleration. In one run, position vs. time graph VI is produced. Which velocity vs. time graph is produced by this run?
II, The slope of the position vs time graph starts out upward, so the initial velocity must be positive. The position vs. time graph curves downward like a frown, so the acceleration is negative, meaning the slope of the velocity vs. time graph must be downward.
An experiment uses a fan cart to study motion with constant acceleration. In one run, position vs. time graph I is produced. Which velocity vs. time graph is produced by this run?
III, The slope of the position vs time graph starts out horizontal, so the initial velocity must be zero. The position vs. time graph curves upward like a smile, so the acceleration is positive, meaning the slope of the velocity vs. time graph must be upward.
An experiment uses a fan cart to study motion with constant acceleration. In one run, position vs. time graph IV is produced. Which velocity vs. time graph is produced by this run?
IV, The slope of the position vs time graph starts out downward, so the initial velocity must be negative. The position vs. time graph curves upward like a smile, so the acceleration is positive, meaning the slope of the velocity vs. time graph must be upward.
How long is the line that's drawn
Pinky nail is about 1cm.
An experiment uses a fan cart to study motion with constant acceleration. In one run, position vs. time graph III is produced. Which velocity vs. time graph is produced by this run?
V, The slope of the position vs time graph starts out downward, so the initial velocity must be negative. The position vs. time graph curves downward like a frown, so the acceleration is negative, meaning the slope of the velocity vs. time graph must be downward.
An experiment uses a fan cart to study motion with constant acceleration. In one run, position vs. time graph II is produced. Which velocity vs. time graph is produced by this run?
VI, The slope of the position vs time graph starts out upward, so the initial velocity must be positive. The position vs. time graph curves downward like a frown, so the acceleration is negative, meaning the slope of the velocity vs. time graph must be downward.
Consider a ball of mass m rolling down an inclined plane. The normal force on the ball a) is equal to mg, always. c) is greater than mg, always. b) may be greater or less than mg. d) is less than mg, always.
d
