CYU physics 180A
the blades of a ceiling fan start from rest and, after two revolutions have an angular speed of 0.5 rev/s. the angular acceleration of the blades is constant. what is the angular speed after eight revolutions?
1.0 rev/s SOLUTION: 2rev= 12.566rad= x 0.5 rev/s= 3.14rad/s = Vf Vi=0 xf= xo + (1/2)[(vo+vf)(t)] t=(x)/(Vf)= (12.566) / 2(0+3.14) = 8s a= (Vf - Vo)/t = (3.14 - 0) / 8 = 0.3927 rev/s s= 8(2pi) = 50.265rad Vf^2 = Vo^2 + 2as Vf = squareroot [2(0.3927)(50.265)] = 6.283 rad/s convert to rev/s (6.283 rad/s)(1rev) / (2pi) = 1 rev/s
a box has a weight of 150N and is being pulled across a horizontal floor by a force that has a magnitude of 110N. the pulling force can point horizontally, or it can point above the horizontal at an angle theta. when the pulling force points horizontally, the kinetic frictional force acting on the box is twice as large as when the pulling force points at the angle theta. find theta.
43deg
three objects are visible in the night sky. they have the following diameters (in multiples of d) and subtend the following angles (in multiples of theta) at the eye of the observer. object A has a diameter of 4d and subtends an angle of 2theta. object B has a diameter of 3d and subtends an angle of theta/2. object C has a diameter of d/2 and subtends an angle of theta/8. rank them in descending order (greatest first) according to their distance from the observer.
B C A
the blade of a lawn mower is rotating at an angular speed of 17 rev/s. the tangential speed of the outer edge of the blade is 32 m/s. what is the radius of the blade?
SOLUTION: w = 17(2pi) = 106.814 rad/s Vt = 32 m/s Vt = (r)(w) r = 32 / 106.814 ********* r = 0.3 m **********
a 10kg suitcase is placed on a scale that is in an elevator. in which direction is the elevator accelerating when the scale reads 75N and when it reads 120N? a) downward when it reads 75N and upward when it reads 120N b) upward when it reads 75N and downward when it reads 120N c) downward in both cases d) upward in both cases
a
a rope is used in a tug of war between two teams of five people each. both teams are equally strong, so neither team wins. an identical rope is tied to a tree, and the same ten people pull it just as hard on the loose end as they did in the contest. in both cases, the people pull steadily with no jerking. which rope sustains the greater tension? a) the rope tied to the tree b) the rope in the tug of war c) the ropes sustain the same tension
a
a suitcase is hanging straight down from your hand as you ride an escalator. your hand exerts a force on the suitcase, and this force does work. this work .. a) positive when you ride up and negative when you ride down b) negative when you ride ujp and positive when you ride down c) positive when you rude up or down d) negative when you ride up or down
a
an experimental vehicle slows down and comes to a halt with an acceleration whose magnitude is 9.8 m/s2. after reversing direction in a negligible amount of time, the vehicle speeds up with an acceleration of 9.8 m/s2. except for being horizontal, is the motion: a) the same as or b) different ..............from the motion of a ball that is thrown straight upward, comes to a halt, and falls back down to earth?
a
it is possible to build a clock in which the tips of the hour hand and the second hand move with the same tangential speed. this is normally never done, however. why? a) the length of the hour hand would be 3600 times greater than the length of the second hand b) the hour hand and the second hand would have the same length c) the length of the hour hand would be 3600 times smaller than the length of the second hand
a
starting in the spring, fruit begins to grow on the outer end of a branch on a pear tree. as the fruit grows, does the center of gravity of the pear-growing branch a) move toward the pears at the end of the branch b) move away from the pears c) not move at all
a
water, dripping at a constant rate from the faucet, falls to the ground. at any instant there are many drops in the air between the faucet and the ground. where does the center of mass of the drops lie relative to the halfway point between the faucet and the ground? a) above it b) below it c) exactly at the halfway point
a
two vectors A and B are added together to give a resultant vector R: R=A+B. the magnitudes of A and B are 3m and 8m, respectively, but the vectors can have any orientation. what are..... a) the max possible value b) the min possible value ............................................for the magnitude of r?
a) 11m b) 5m
two uniform solid balls are placed side by side at the top of an incline plane and, starting from rest, are allowed to roll down the incline. which ball, if either, has the greater translational speed at the bottom if... a) they have the same radii, but one is more massive than the other b) they have the same mass, but one has a larger radius
a) both have the same translational speed b) both have the same translational speed
a woman is sitting on the spinning seat of a piano stool with her arms folded. ignore any friction in the spinning stool. what happens to her a) angular velocity b) angular momentum ........... when she extends her arms outward??
a) decreases b) remains the same
an ice boat is coasting on a frozen lake. friction between the ice and the boat is negligible, and so is air resistance. nothing is propelling the boat. from a bridge someone jumps straight down into the boat, which continues to coast straight ahead. a) does the total horizontal momentum of the boat plus the jumper change? b) does the speed of the boat itself increase, decrease, or remain the same?
a) no b) decrease
an object slides along the surface of the earth and slows down because of kinetic friction. if the object alone is considered as the system, the kinetic frictional force must be identified as an external force that decreases the momentum of the system. a) if both the object and the earth are considered to be the system, is the force of kinetic friction still an external force? b) can the frictional force change the total linear momentum of the two-bodied system?
a) no b) no
an airplane is flying horizontally with a constant momentum during a time interval (delta) t. a) is there a net impulse acting on the plane during this time? b) in the horizontal direction, both the thrust generated by the engines and air resistance act on the plane. considering your answer to part a, how is the impulse of the thrust related (in magnitude and direction) to the impulse of the force due to the air resistance?
a) no b) the impulse of the thrust is equal in magnitude and opposite in direction to the impulse of the force due to air resistance
a space probe is initially moving with a constant translational velocity and a zero angular velocity. a) when the two engines are fired, each generating a thrust of magnitude T, does the translational velocity increase, decrease, or remain the same? b) does the angular velocity increase, decrease, or remain the same?
a) remains the same b) increases
at a given instant an object has an angular velocity. it also has an angular acceleration due to torques that are present. therefore, the velocity at this instant increases, decreases or remain the same.... a) if additional torques are applied so as to make the net torque suddenly equal to zero and b) if all the torques are suddenly removed
a) remains the same b) remains the same
vectors A and B satisfy the vector equation A+B=0. a) how does the magnitude of B compare with the magnitude of A? b) how does the direction of B compare with the direction of A?
a) the magnitude of B is equal to the magnitude of A b) the direction of B is opposite the direction of A
a tennis ball is hit upward into the air and moves along an arc. neglecting air resistance, where along the arc is the speed of the ball... a) minimum b) maximum
a) when the ball is at its highest point in the trajectory b) at the initial and final positions of motion
two objects have the same momentum. do the velocities of these object necessarily have... a) the same directions and b) the same magnitudes?
a) yes b) no
is it possible a) for a large force to produce a small, or even zero torque? and b) for a small force to produce a large torque
a) yes, if the lever arm is very small b) yes, if the lever arm is very large
a sunbather is lying on a floating raft that is stationary. she then gets up and walks to one end of the raft. consider the sunbather and the raft as an isolated system. a) what is the velocity of the center of mass of this system while she is walking? b) does the raft itself move while she is walking? if so, what is the direction of the rafts velocity relative to that of the sunbather?
a) zero b) yes, opposite to the motion of the sunbather
the earth rotates once per day about its axis, which is perpendicular to the plane of the equator and passes through the north geographic pole. where on earths surface should you stand in order to have the smallest possible tangential speed?
at the north or south pole
a straight track is 1600m in length. a runner begins at the starting line, runs due east for the full length of the track, turns around and runs halfway back. the time for his run is 5min. what is the runners average velocity and his average speed?
avg. velocity = 2.7 m/s due east avg. speed = 8 m/s
a thin sheet of plastic is uniform and has the shape of an equilateral triangle. consider two axes for rotation. both are perpendicular to the plane of the triangle, axis A passing through the center of the triangle and axis B passing through one corner. if the angular speed w about each axis is the same, for which axis, does the triangle have the greater rotational KE?
axis B
equation (theta=wot+1/2at^2) is beig used to solve a problem in rotational kinematics. which one of the following sets of values for the variables wo, a, and t cannot be substituted directly into this equation to calculate a value for theta? a) wo = 1.0 rad/s , a = 1.8 rad/s^2 , and t= 3.8s b) wo = 0.16 rev/s , a = 1.8 rad/s^2 , and t= 3.8s c) wo = 0.16 rev/s , a = 0.29 rev/s^2 , and t= 3.8s
b
in baseball, the pitchers mound is raised to compensate for the fact that the ball falls downward as it travels from the pitcher toward the batter. is the baseball were played on the moon, would the pitchers mound have to be... a) higher than b) lower than c) the same height......... as on earth?
b
suppose you are driving due east, traveling a distance of 1500m in 2min. you then turn due north and travel the same distance in the same time. what can be said about the average speeds and the average velocities for the two segments of the trip? a) the average speeds are the same, and the average velocities are the same b) the average speeds are the same, but the average velocities are different c) the average speeds are different, but the average velocities are the same
b
suppose you are standing on the edge of a dock and jump straight down. if you land on sand your stopping time is much shorter than if you land on water. using the impulse-momentum theorem as a guide, determine which one of the following statements is correct: a) in bringing you to a half, the sand exerts a greater impulse on you than the water does b) in bringing you to a half, the sand and the water exert the same impulse on you c) in bringing you to a half, the sand and the water exert the same impulse on you, but the sand exerts a smaller average force
b
when a body is moved from sea level to the top of a mountain, what changes? a) the bodys mass b) its weight c) both mass and weight
b
in movies, superman hovers in midair, grabs a villain by the neck, and throws him forward. superman, however, remains stationary. this is not possible, because it violates: a) the law of conservation of energy b) newtons 2nd law c) newtons 3rd law d) the principle of conservation of linear momentum
b, c, and d
which of the following statements, if any, involves a vector? a) i walked 2 miles along the beach b) i walked 2 miles due north along the beach c) i jumped off a cliff and hit the water traveling at 17 mi/hr d) i jumped off a cliff and hit the water traveling straight down at a speed of 17 mi/hr e) my bank account shows a negative balance of $-25
b, d
two balls are launched upward from the same spot at different angles with respect to the ground. both balls rise to the same max height. ball A, however, follows a trajetory that has a greater range than that of ball B. ignoring air resistance, decide which ball, if either, has the greater launch speed.
ball A has the greater launch speed
bob and bill have the same weight and wear identical shoes. when they both keep their feet flat on the floor and their bodies straight, bob can lean forward farther than bill can before falling. other things being equal, whose center of gravity is closer to the ground when both are standing erect?
bob
a ball has a speed of 15 m/s. only one external force acts on the ball. after this force acts, the speed of the ball is 7 m/s. has the force done... a) positive b) zero c) negative ........... work on the ball?
c
a building is located on the earths equator. as the earth rotates about its axis, which floor of the building has the greatest tangential speed? a) the first floor b) 10th floor c) 20th floor
c
a circus performer hangs stationary from a rope. she then begins to climb upward by pulling herself up, hand over hand. when she starts climbing, is the tension in the rope.... a) less than b)equal to c) greater than..... it is when she hangs stationary?
c
a power boat, starting from rest, maintains a constant acceleration. after a certain time t, its displacement and velocity are r and v. at time 2t, what would be its displacement and velocity, assuming the acceleration remains the same? a) 2r and 2v b) 2r and 4v c) 4r and 2v d) 4r and 4v
c
an electric clock is hanging on the wall. as you are watching the second hand rotate, the clocks battery stops functioning, and the second hand comes to a halt over a brief period of time. which one of the following statements correctly describes the angular velocity w and the angular acceleration a of the second hand as it slows down? a) w and a are both negative b) w is positive and a is negative c) w is negative and a is positive d) w and a are both positive
c
suppose two objects collide head on where initially object 1 (mass=m1) is moving and object 2 (mass=m2) is stationary. now assume that they have the same mass, so m1=m2. which one of the following statements is true? a) both objects have the same velocity (magnitude and direction) after the collision b) object 1 rebounds with one-half its initial speed, while object 2 moves to the right with one half the speed that object 1 had before the collision c) object 1 stops completely, while object 2 acquires the same velocity (magnitude and direction) that object 1 had before the collision
c
a thin rod rotates at a constant angular speed. in case A the axis of rotation is perpendicular to the rod at its center. in case B the axis is perpendicular to the rod at one end. in which case, if either, are there points on the rod that have the same tangential speeds?
case A
a car is up on a hydraulic lift at a garage. the wheels are free to rotate, and the drive wheels are rotating with a constant angular velocity. which of the following statements is true? a) a point on the rim has no tangential and no centripetal acceleration b) a point on the rim has both a nonzero and tangential acceleration and a nonzero centripetal acceleration c) a point on the rim has a nonzero tangential acceleration but no centripetal acceleration d) a point on the rim has no tangential acceleration but does have a nonzero centripetal acceleration
d
suppose the ice cap at the south pole were to melt and the water distributed uniformly over the earths oceans. would the earths angular velocity increase, decrease, or remain the same?
decrease
you are a passenger on a jetliner that is flying at a constant velocity. you get up from your seat and walk toward the front of the plane. because of this action, your forward momentum increases. does the forward momentum of the plane itself decrease, remain the same, or increase?
decrease
a satellite explodes in outer space, far from any other body, sending thousands of pieces in all directions. is the linear momentum of the satellite before the explosion less than, equal to, or greater than the total linear momentum of all the pieces after the explosion?
equal to
rolling motion is an example that involves rotation about an axis that is not fixed. give three other example of rotational motion about an axis that is not fixed
ex from the book ) 1. motions of a frisbee through the air 2. a twirling baton that has been thrown into the air 3. the blades on a moving lawn mower cutting the grass 4. an ice skater performing a quadruple jump
a cloud of interstellar gas is rotating. because the gravitational force pulls the gas particles together, the cloud shrinks, and, under the right conditions, a star may ultimately be formed. would the angular velocity of the star be less than, equal to, or greater than the angular velocity of the rotating gas?
greater than
sometimes, even with a wrench, one cannot loosen a nut that is frozen tightly to a bolt. it is often possible to loosen the nut by slipping one end of a long pipe over the wrench handle and pushing at the other end of the pipe. with the aid of the pipe, does the applied force produce a smaller torque, a greater torque, or the same torque on the nut?
greater torque
two objects are thrown vertically upward, first one, and then, a bit later, the other. is it possible or impossible that both objects reach the maximum height at the same instant of time?
impossible
the speedometer of a truck is set to read the linear speed of the truck, but uses a device that actually measures the angular speed of the rolling tires that came with the truck. however, the owner replaces the tires with larger-diameter versions. does the reading on the speedometer after the replacement give a speed that is less than, equal to, or greater than the true linear speed of the truck?
less than
uniform circular motion of a space station can be used to create artificial gravity. this can be done by adjusting the angular speed of the space station, so the centripetal acceleration at an astronauts feet equals g, the magnitude of the acceleration due to the earths gravity. if such an adjustment is made, will the acceleration at the astronauts head due to the artificial gravity be greater than, equal to, or less than g?
less than
would you expect the center of mass of a baseball bat to be located halfway between the ends of the bat, nearer the lighter end, or nearer the heavier end?
nearer the heavier end
a freight train is accelerating on a level track. other things being equal, would the tension in the coupling between the engine and the first car change if some of the cargo in the last car were transferred to any one of the other cars?
no
a person is hanging motionless from a vertical rope over a swimming pool. she lets go of the rope and drops straight down. after letting go, is it possible for her to curl into a ball and start spinning?
no
a runner runs half the remaining distance to the finish line every ten seconds. she runs in a straight line and does not ever reverse her direction. does her acceleration have a constant magnitude?
no
a sailboat is moving at a constant velocity. is work being done by a net external force acting on the boat?
no
are two vectors with the same magnitude necessarily equal?
no
can a single object have a KE but no momentum?
no
can two nonzero perpendicular vectors be added together so their sum is zero?
no
in the equation y=(c^n)(a)(t^2) you wish to determine the integer value of the exponent n. the dimensions of y, a, and t are known. it is also known that c has no dimensions. can dimensional alaysis be used to determine n?
no
a pair of scissors is being used to cut a piece of paper in half. does each blade of the scissors have the same angular velocity (both magnitude and direction) at a given instant?
no because the instantaneous angular speed of each blade is the same, but the blades are rotating in opposite directions
in an elastic collision, is the KE of each object the same before and after the collision?
no. it is the total KE of the system that is the same before and after the collision
a stone is thrown from the top of a cliff. air resistance is negligible. as a stone falls, is it in equilibrium or not?
not in equilibrium
a rotating object starts from rest and has a constant angular acceleration. three seconds later the centripetal acceleration of a point on the object has a magnitude of 2 m/s^2. what is the magnitude of the centripetal acceleration of this point six seconds after the motion begins?
rw^2 = 2 m/s^2 wo = 0 a = v^2 / r = rw^2 w = wo + at w at (t=3) = 3a -----> r(3a)^2 = 2 after 6 seconds.... w = wo + 6a = 6a rw^2 (at t=6) = r(6a)^2 = r[2(3a)]^2 = 4r(3a)^2 = 4[r(3a)^2] = 8 m/s^2
a hoop, a solid cylinder, a spherical shell, and a solid sphere, are placed at rest at the top of an incline. all the objects have the same radius. they are then released at the same time. what is the order in which they reach the bottom (fastest first)?
solid sphere solid cylinder spherical shell hoop
a woman is struggling to keep a stack of boxes balanced on a dolly. the womans left foot is on the axle of the dolly. assuming that the boxes are identical, which one creates the greatest torque with respect to the axle?
the box at the far right of the dolly
the energy released by the exploding gunpowder in a cannon propels the cannonball forward. simultaneously, the cannon recoils. the mass of the cannonball is less than that of the cannon. which has the greater KE, the launched cannonball or the recoiling cannon? assume that momentum conservation applies.
the cannonball
a person has a choice of either pushing or pulling a sled at a constant velocity. friction is present. if the angle theta is the same in both cases, does it require less force to push or to pull the sled?
to pull, because the upward component of the pulling force reduces the normal force and therefore also reduces the force of kinetic friction acting on the sled
the vectors A, B, and C satisfy the vector equation A+B=C, and their magnitudes are related by the scalar equation A^2 + B^2 = C^2. how is vector A oriented with respect to vector B?
vector A is perpendicular to vector B
the vectors A, B, and C satisfy the vector equation A+B=C, and their magnitudes are related by the scalar equation A+B=C. how is vector A oriented with respect to vector B?
vector A points in the same direction as vector B
can a group of two or more object have a total KE that is not zero but a total momentum that is zero?
yes
on a distant asteroid, a large catapult is used to throw chunks of stone into space. could such a device be used as a propulsion system to move the asteroid closer to the earth?
yes
the muzzle velocity of a gun is the velocity of the bullet when it leaves the barrel. the muzzle velocity of one rifle with a short barrel is greater than the muzzle velocity of another rifle that has a longer barrel. in which rifle is the acceleration of the bullet larger?
the rifle with the shorter barrel
a penny is placed on a rotating turntable. where on the turntable does the penny require the larges centripetal force to remain in place: at the center of the turntable or at the edge of the turntable?
the edge of the turntable
consider two people, one on the earths surface at the equator and the other at the north pole. which has the larger centripetal acceleration?
the person at the equator
what is the chance of a light car safely rounding an unbanked curve on an icy road as compared to that of a heavy car: worse, the same, or better? assume that both cars have the same speed and are equipped with identical tires.
the same
in times square in new york city, people celebrate on NYE. some just stand around, but many move about randomly. consider a group consisting of all of these people. approximately, what is the total linear momentum of this group at any given instant?
the total linear momentum is approximately zero because of the random directions and random speeds of the moving people
a plane takes off at st. louis, flies to denver, and then returns the same way. the plane flies at the same speed with respect to the ground during the entire flight, and there are no head winds or tail winds. since the earth revolves around its axis once a day, you might expect that the times for the outbound trip and the return trip differ, depending on whether the plane flies against the earths rotation or with it. is this true, or are the two times the same?
the two times are the same
a stone is tied to a string and whirled around in a circle at a constant speed. is the string more likely to break when the circle is horizontal or when it is vertical? assume that the constant speed is the same in each case.
vertical
a wrench is accidentally dropped from the top of the mast on a sailboat. air resistance is negligible. will the wrench hit at the same place on the deck whether the sailboat is at rest or moving with a constant velocity?
yes
can 3+ vectors with unequal magnitudes be added together so their sum is zero?
yes
is it possible for two quantities to have the same dimensions but different units?
yes
the average velocity for a trip has a positive value. is it possible for the instantaneous velocity at a point during the trip to have a negative value?
yes
the magnitude of a vector has doubled, its direction remaining the same. can you conclude that the magnitude of each component of the vector has doubled?
yes
object A weighs twice as much as object B at the same spot on the earth. would the same be true at a given spot on Mars?
yes, because the ratio of the two weights depends only on the masses of the objects, which are the same on earth and on mars
the speedometer of your car shows that you are traveling at a constant speed of 35 m/s. is it possible that your car is accelerating?
yes, if you are going around a curve
other things being equal, would it be easier to drive at a high speed around an unbanked horizontal curve on the moon than to drive the same curve on earth?
no
at one instant of time, a car and a truck are traveling side by side in adjacent lanes of a highway. the car has a greater velocity than the truck has. does the car necessarily have a greater acceleration?
no
is it correct to conclude that one engine is doing twice the work that another is doing just because it is generating twice the power? a) yes b) no
no
is it possible for two quantities to have the same units but different dimensions?
no
is the acceleration of a projectile equal to zero when the projectile reaches the top of its trajectory?
no
a honeybee leaves the hive and travels a total distance of 2km before returning to the hive. what is the magnitude of the displacement vector of the bee?
0 meters
a motorcycle starts from rest and has a constant acceleration. in a time interval (t), is undergoes a displacement (x) and attains a final velocity (v). then t is increased so that the displacement is 3x. in this same increased time interval, what final velocity does the motorcycle attain?
1.73v
engine A has a greater power rating than engine B. which one of the following statements correctly describes the abilities of these engines to do work? a) engines A and B can do the same amount of work, but engine A can do it more quickly b) engines A and B can do the same amount of work in the same amount of time c) in the same amount of time, engine B can do more work than engine A
a
in a simulation on earth, an astronaut in his space suit climbs up a vertical ladder. on the moon, the same astronaut makes the exact same climb. which one of the following statements correctly describes how the gravitational potential energy of the astronaut changes during the climb? a) it changes by a greater amount on the earth b) it changes by a greater amount on the moon c) the change is the same in both cases
a
in which of the following situations could an object possibly be in equilibrium? a) three forces act on the object; the forces all point along the same line but may have different directions b) two perpendicular forces act on the object c) a single force acts on the object d) in none of the situations described in a, b, and c could the object possibly be in equilibrium
a
three particles have identical masses. each particle experiences on the gravitational forces due to the other two particles. how should the particles be arranged so each on e experiences a net gravitational force that has teh same magnitude? a) on the corners of an equilateral triangle b) on three of the four corners of a square c) on the corners of a right triangle
a
which of the following statements is incorrect? a) the car traveled around the circular track at a constant velocity b) the car traveled around the circular track at a constant speed.
a
which of the following statements about centripetal acceleration is true? a) an object moving at a constant velocity cannot have a centripetal acceleration b) an object moving at a constant speed may have a centripetal acceleration
a and b
a father and his 7 year old daughter are facing each other on ice skates. with their hands, they push off against one another. which one or more of the following statements is/are true? a) each experiences an acceleration that has a different magnitude b) each experiences acceleration of the same magnitude c) each experiences a pushing force that has a different magnitude d) each experiences a pushing force that has the same magnitude
a and d
which of the following displacement vectors are equal? variable magnitude direction A 100m 30deg. N of E B 100m 30deg. S of W C 50m 30deg. S of W D 100m 60deg. E of N
a and d
a car is traveling in a uniform circular motion on a section of road whose radius is r. the road is slippery, and the car is just on the verge of sliding. a) if the cars speed were doubled, what would be the smallest radius at which the car does not slide? express your answer in terms of r. b) what would be your answer in part a if the car were replaced by one that weighted twice as much, the cars speed still being doubled?
a) 4r b) 4r
the tail of a vector is fixed to the origin of an x, y, z axis system. originally the vector points along the +x axis and has a magnitude of 12 units. as time passes, the vector rotates counterclockwise. what are the sizes of the x and y components of the vector for the following rotational angles: a) 90deg. b) 180deg. c) 270deg. d) 360deg.
a) ax= 0 units & ay= 12 units b) ax= -12 units & ay= 0 units c) ax= 0 units & ay= -12 units d) ax= 12 units & ay= 0 units
the acceleration due to gravity on the moon is one-sixth that on earth. a) is the true weight of a person on the moon less than, greater than, or equal to the true weight of the same person on earth? b) is the apparent weight of a person in orbit around the moon less than, greater than, or equal to the apparent weight of the same person in orbit about the earth?
a) less than b) equal to
a stone is thrown horizontally from the top of a cliff and eventually hits the ground below. a second stone is dropped from rest from the same cliff, falls through the same height, and also hits the ground below. ignore air resistance. is each of the following quantities different or the same in the two cases? a) displacement b) speed just before impact with the ground c) time of flight
a) the displacement is greater for the stone thrown horizontally b) the impact speed is greater for the stone thrown horizontally c) the time of the flight is the same for both stones
a child is playing on the floor of a RV as it moves along the highway at a constant velocity. he has a toy cannon, which shoots a marble at a fixed angle and speed with respect to the floor. the cannon can be aimed toward the front or the rear of the RV. is the range toward the font the same as, less than, or greater than the range toward the rear? a) from the childs point of view b) from the point of view of an observer standing still on the ground
a) the range toward the front is the same as the range toward the rear b) the range toward the front is greater than the range toward the rear
would a change in the earths mass affect.. a) the banking of airplanes as they turn b) the banking of roadbeds c) the speeds with which satellites are put into circular orbits d) the performance of the loop-the-loop motorcycle stunt?
a) yes b) yes c) yes d) yes
an object is thrown upward at an angle theta above the ground, eventually returning to earth. a) is there any place along the trajectory where the velocity and acceleration are perpendicular? if so, where? b) is there any place where the velocity and acceleration are parallel? if so, where?
a) yes, when the object is at its highest point b) no
suppose the total mechanical energy of an object is conserved. which one or more of the following statements are is/are true? a) if the KE decreases, the gravitational PE increases b) if the gravitational PE decreases, the KE increases c) if the KE does not change, the gravitational PE also does not change
a, b, and c
The following lists four variables, along with their units: variable units x meters (m) v meters per second (m/s) t seconds (s) a meters per second squared (m/s2) these variables appear in the following equations, along with a few numbers that have no units. in which of the equations are the units on the left side of the equals sign consistent with the units on the right side? a) x=vt b) x=vt+ 1/2at^2 c) v=at d) v=at+ 1/2at^3 e) v^3= 2ax^2 f) t= (2x/a)^1/2
a, b, c, f
a ball is dropped from rest from the top of a building and strikes the ground with a speed Vf. from ground level, a second ball is thrown straight upward at the same instant that the first ball is dropped. the initial speed of the second ball is Vo=Vf, the same speed with which the first ball eventually strikes the ground. ignoring air resistance, decide whether the balls cross paths: a) at half the height of the building b) above the halfway point c) below the halfway point
b
a ball is thrown straight upward with a velocity Vo and in a time t reaches the top of its flight path, which is a displacement y above the launch point. with a launch velocity of 2Vo, what is the time required to reach the top of its flight path and what would be the displacement of the top point above the launch point? a) 4t and 2y b) 2t and 4y c) 2t and 2y d) 4t and 4y e) t and 2y
b
the Kingda Ka roller coaster starts with a speed of 6 m/s at the top of the drop and attains a speed of 50.3 m/s when it reaches the bottom. if the roller coaster were then to start up an identical hill, what speed would it attain when it reached the top? assume that friction and air resistance are absent. a) > 6 m/s b) = 6 m/s c) between 0 m/s and 6 m/s d) 0 m/s
b
which of the following statements can be explained by Newtons 1st law? A) when your car suddenly comes to a halt, you lunge forward ...B) when your car rapidly accelerates, you are pressed backward against the seat a) neither A or B b) both A and B c) A but not B d) B but not A
b
in which one or more of the following situations is the principle of conservation of mechanical energy obeyed? a) an object moves uphill with an increasing speed b) an object moves uphill with a decreasing speed c) an object moves uphill with a constant speed d) an object moves downhill with an increasing speed e) an object moves downhill with a decreasing speed f) an object moves downhill with a constant speed
b and d
a rifle, at a height H above the ground, fires a bullet parallel to the ground. at the same instant and the same height, a second bullet is dropped from rest. in the absence of air resistance, which bullet, if either, strikes the ground first?
both bullets reach the ground at the same point
a net external force acts on a particle that is moving along a straight line. this net force is not zero. which one of the following statements is correct? a) the velocity, but not the kinetic energy, of the particle is changing b) the kinetic energy, but not the velocity, of the particle is changing c) both the velocity and the kinetic energy of the particle are changing
c
all of the following, except one, cause the acceleration of an object to be double. which one is the exception? a) all the forces acting on the object double b) the net force acting on the objects double c) both the net force acting on the object and the mass of the object double d) the net force acting on the object remains the same, while the mass of the object is reduced by a factor of two
c
in one case, a sports car, its engine running, is driven up a hill at a constant speed. in another case, a truck approaches a hill, and its driver turns off the engine at the bottom of the hill. the truck then coasts up the hill. which vehicle is obeying the principle of conservation of mechanical energy? a) both car and truck b) only the car c) only the truck
c
suppose that the coefficients of static and kinetic friction have values such that ms= 1.4mk for a crate in contact with a cement floor. which one of the following statements is true? a) the magnitude of the static frictional force is always 1.4 times the magnitude of the kinetic frictional force b) the magnitude of the kinetic frictional force is always 1.4 times the magnitude of the static frictional force c) the magnitude of the max. static frictional force is 1.4 times the magnitude of the kinetic frictional force
c
the net external force acting on an object is zero. which of the following statements is true? a) the object can only be stationary b) the object can only be traveling with a constant velocity c) the object can either be stationary or traveling with a constant velocity d) the object can only be traveling with a velocity that is changing
c
two cars are moving in the same direction (the positive direction) on a straight road. the acceleration of each car also points in the positive direction. car 1 has a greater acceleration than car 2 has. which of the following statements is true? a) the velocity of car 1 is always greater than the velocity of car 2 b) the velocity of car 2 is always greater than the velocity of car 1 c) in the same time interval, the velocity of car 1 changes by a greater amount than the velocity of car 2 does d) in the same time interval, the velocity of car 2 changes by a greater amount than the velocity of car 1 does
c
a box rests on the floor of an elevator. because of static friction, a force is required to start the box sliding across the floor when the elevator is a) stationary b) accelerating upward c) accelerating downward rank the forces required in these three situations in ascending order (small --> large)
c, a, b
two cars are identical, except for the type of thread design on their tires. the cars are driven at the same speed and enter the same unbanked horizontal turn. car A cannot negotiate the turn, but car B can. which threat design, the one on car A or the one on car B, yields a larger coefficient of static friction between the tires and the road?
car B
a box is being moved with a velocity v by a force P (in the same direction as v) along a level horizontal floor. the normal force is Fn, the kinetic frictional force is fk, and the same weight is mg. which one of the following statements is correct? a) P does positive work, Fn and fk do zero work, and mg does negative work. b) Fn does positive work, P and fk do zero work, and mg does negative work c) fk does positive work, Fn and mg do zero work, P does negative work d) P does positive work, Fn and mg do zero work, and fk does negative work
d
a force does positive work on a particle that has a displacement pointing in the +x direction. this same force does negative work on a particle that has a displacement pointing in the +y direction. in which quadrant of the x, y coordinate system does the force lie? a) first b) second c) third d) fourth
d
during the final stages of descent, a sky diver with an open parachute approaches the ground with a constant velocity. there is no wind to blow him from side to side. which one of the following statements is true? a) the sky diver is not in equilibrium b) the force of gravity is the only force acting on the sky diver, so that he is in equilibrium c) the sky diver is in equilibrium because no forces are acting on him d) the sky diver is in equilibrium because two forces act on him, the downward acting force of gravity and the upward acting force of the parachute
d
in case A an object is moving straight downward with a constant speed of 9.8 m/s, while in case B an object is moving straight downward with a constant acceleration of magnitude of 9.8 m/s2. which one of the following is true? a) a nonzero net external force acts on the object in both cases b) a nonzero net external force acts on the object in neither case c) a nonzero net external force acts on the object in case A only d) a nonzero net external force acts on the object in case b only
d
a net external nonconservative force does positive work on a particle. based solely on this info, you are justified in reaching only one of the following conclusions. which one is it? a) the KE and PE of the particle both decrease b) the KE and PE of the both increase c) neither the KE nor the PE of the particle changes d) the total mechanical energy of the particle decreases e) the total mechanical energy of the particle increases
e
a rocket is at rest on the launch pad. when the rocket is launched, its kinetic energy increases. consider all of the forces actin on the rocket during the launch, and decide whether the following statement is true or false: the amount by which the kinetic energy of the rocket increases during the launch is equal to the work done by the force generated by the rockets engine
false
two satellites are placed in orbit, one about mars and the other one about jupiter, such that the orbital speeds are the same. mars has the smaller mass. is the radius of the satellite in orbit about mars less than, greater than, or equal to the radius of the satellite orbiting jupiter?
less than
a leopard springs upward at a 45deg. angle and then falls back to the ground. air resistance is negligible. does the leopard, at any point on its trajectory, ever have a speed that is one half its initial value?
no
a vector has a component of zero along the x axis of a certain axis system. does this vector necessarily have a component of zero along the x axis of another (rotated) axis system?
no
an object moving with a constant acceleration slows down if the acceleration points in the direction opposite to the direction of the velocity. but can an object ever come to a permanent halt if its acceleration truly remains constant?
no
on a riverboat cruise, a plastic bottle is accidentally dropped overboard. a passenger on the boat estimates that the boat pulls ahead of the bottle by 5m per each second. is it possible to conclude that the magnitude of the velocity of the boat with respect to the shore is 5 m/s?
no
two buses depart from chicago, one going to new york and one to san francisco. each bus travels at a speed of 30m/s. do they have the same velocities?
no
two identical automobiles have the same speed, one traveling east and one traveling west. do these cars have the same momentum?
no
you can always add two number that have the same units (such as 6 meters + 3 meters). Can you always add two numbers that have the same dimensions, such as two numbers that have the dimensions of length (L)?
no
a stack of books whose true weight is 165N is placed on a scale in an elevator. the scale reads 165N. from this information alone, can you tell whether the elevator is moving with a constant velocity of 2 m/s upward, is moving with a constant velocity of 2 m/s downward, or is it at rest?
no you cannot tell
a crate hangs from a ring in the middle of a rope. a person is pulling on the right end of the rope to keep the crate in equilibrium. can the rope ever be made perfectly horizontal?
no, because there must always be a vertical (upward) component of the tension force in the rope to balance the weight of the crate
newtons 2nd law indicates that when a net force acts on an object, it must accelerate. does this mean that when two or more forces are applied to an object simultaneously, it must accelerate?
no, because two or more forces can cancel each other, leading to a net force of zero
is the average speed of a vehicle a vector or a scalar quantity?
scalar
three swimmers can swim equally fast relative to the water. they have a race to see who can swim across a river in the least time. swimmer A swims perpendicular to the current and lands on the far shore downstream, because the current has swept him in that direction. swimmer B swims upstream at an angle to the current, choosing the angle so that he lands on the far shore directly opposite the starting point. swimmer C swims downstream at an angle to the current in attempt to take advantage of the current. who crosses the river in the least amount of time?
swimmer A
