BYU p121
carrying 5 kg bucket dashes 5m across yard at constant speed of 4m/s. how much work was done on the bucket in that process?
0 joules (There is no change in kinetic energy, so there is no work done on the bucket. The gravitational force is perpendicular to the displacement.) (w=fd and no net force on horizontal so w=0) cm7
to convert the speed of 14.5 fulongs/fortnight to meters/second, you should multiply which of the following conversion factors times 14.5 furlongs/fortnights?
1 fortnight/14 days 1 day/86400 seconds 201.168 m/ 1 fulong cm1
which of the following principles makes it possible to calculate a vector sum by breaking the vector into its components?
1. sum of 2 vectors pointing in the same direction is in that same direction 2. magnitude of sum of 2 vectors in the same direction is equal to the sum of magnitude of the 2 vectors 3. magnitude of sum of 2 vectors in directly opposite directions is equal to the difference of magnitude of the 2 vectors 4. a vector perpendicular to a given vector has no component in the direction of the given vector cm3
what is true
1. work done by conservative force only depends on initial and final states 2. example of nonconservative force is friction 3. work done by nonconservative force depends on path taken cm7
a satellite moves in a very elliptical orbit, such that at the farthest point from earth it feels 1/4 the gravitational force that it feels at the nearest point to the earth. at that highest point, it has what fraction of the gravitational potential compared to the nearest point?
1/2 ( The potential goes as 1/r and the force goes as 1/r2. If the force is 1/4 of what it was, then the potential is 1/2 of it was because 1/4 is 1/2 squared.) cm13
car traveling at 20mph stops in distance of 15 ft when brakes locked. assume frictional force doesn't depend on speed, the same car traveling at 60 mph will stop in distance close to
135 ft (The energy to be dissipated by the frictional force is proportional to v2. The energy is 9 times higher. The work done by friction is proportional to distance traveled, so the distance travel is 9 times longer.) cm8
two objects have same size but different masses. body a has 4 times mass of body b. they are falling through air, which means that the air resistance is proportional to v^2. the terminal velocity of a will be how many times the terminal velocity of b?
2 ( The resistive force from the air must be four times as large on body A as on body B. Since the velocity is two times as large for body A, then the resistive force is 4 times as large, because the air resistance is proportional to v2. This matches the requirements.) cm6
the number of standard helium balloons that can be put into a minivan is closest to
200 cm1
vectors A,B,C. A points west, B points north, C points due east. we don't know their relative magnitudes. we find the cross product of each these vectors with a vector which points due south D. rank the three cross products ( A*D, B*D, C*D) from smallest to largest in terms of their vertical component, taking the sign of the component into account
C*D, B*D, A*D ( The vertical component of ad is positive and that of cd is negative. bd is zero.) cm11
A book is moving to the right across a table at constant speed. There are four forces acting on it, its weight, W, which is straight down, the normal force of the table, N, which is straight up, and two applied forces, one, called F1, pointing 60º to the right of vertical and the other, F2, pointing 60º to the left of vertical. List each of these forces in the order of increasing work, i.e. first list the force which does the least work, then the second most, until you reach the one that does the most work. Two forces that do equal work should have an equal sign between them. Note that we are asking for the ranking to be done by the amount of work, not by the magnitude of the amount of work.
F2 < W = N < F1 ( F2 does negative work, W and N both do zero work and F1 does positive work.) cm7
three axes of rotation. arrange order of smallest to largest moment of inertia for the object. all of the masses are the same and the rods are considered to be massless
The moment of inertia is the [[sum of the masses times their distances squared.]]] Since the masses are all the same, the distances are all that differ. The masses on average are closest to axis II because the horizontal arms are shortest. The masses are on average farthest from axis III because none of the masses lie on that axis. 10cm
two boys on waterslide. one boy (a) slips off top tower and falls unobstructed into pool. at same moment boy b starts sliding down he slide and lands in pool. ignore air resistance and friction, which boy will splash into water first and which will have greater speed when hitting water?
a hits first and has same speed as b (By conservation of energy the two will have the same speed when the arrive because they have fallen the same distance. Boy A has a larger vertical acceleration, so he will arrive first.) cm8
a cannonball is shot horizontally from the top of a tower at the same time another cannonball is dropped from the same height on the tower. the ground is level and ignore air resistance. the cannonball which is dropped hits the ground with
a lower speed and at the same time as the other cannonball cm4
in order to change the angular momentum of an object, it is necessary to apply
a net torque to the object ( A net torque produces a change in angular momentum. If you apply two equal and opposite forces to an object it is possible to have a net torque but no net force.) cm11
which operation is not mathematically allowed?
addition of a vector and a scalar (a vector has direction and a scalar does not) cm3
which of the following is not accelerating?
all are accelerating 1. an object falling freely under influence of gravity 2. a car stopping 3. ball on the end of string moving with constant speed around a circle (direction of the velocity vector is constantly changing in a circle.) 4. a car speeding up going around a curve cm4
a football is thrown by quarterback from shoulder level to a receiver downfield who catches it at shoulder height. at what point in the football motion is its speed a minimum?
at the top of trajectory (the speed is minimum when y component of velocity is at a minimum, because x component of velocity is constant. the y component of the velocity is zero at peak) cm4
whia driver on a trip recorded the reading on his odometer on his car at the beginning and end of his trip. he takes the difference between those two numbers and divides it by the time that the trip took. the quantity he has calulated
average speed cm2
when a pendulum swings with a small angel its motion is approximately simple harmonic. when it swings at at larger angel, why does this not work any more?
because acceleration is no longer proportional to the displacement ( The force, and therefore the acceleration, is proportional to the sine of the displacement, not the displacement. They are approximately equal at small angles, but become increasingly different at large angles.) cm14
a body is made up of multiple parts that are attached to each other by several compressed springs. it has been shot from a cannon and at the peak of its trajectory the springs are released, causing the parts to fly apart. the center of mass of the two parts
continues along the same parabolic path as before 9cm
an isolated rigid body has a single force applied to it. from this we can conclude that it will
definitely have a linear acceleration and possibly have an angular acceleration ( F = ma requires an acceleration if there is a net force, as there must be in this case. If the force is applied at the center of mass then there would be no torque and therefore no angular acceleration. If the force is off the center of mass, then there would be an angular acceleration.) 10cm
average speed of an object during a specified period of time is
equal to the magnitude of the average velocity for the same time period if the direction of motion does not change cm2
a point of stable equilibrium
has a force that points back toward that point regardless of how you leave it cm7
when a car tire rotates about a fixed axis, every portion of the wheel
has the same angular velocity, but different centripetal acceleration ( Every point on a rigid body has the same angular velocity, w. The centripetal acceleration depends on radius: ac = r w2.) 10cm
a student pushes a box across a level floor. student pushes downward at an angle of 30 below the horizontal and friction is important. in this situation the magnitude of frictional force
increase when the student pushes harder (When the student pushes harder there is a downward component to the push. In order to not sink into the floor the normal force must increase. This therefore increases the kinetic friction.) cm5
a driver who is protected by an air bag during a head-on collision is less likely to be seriously injured than an unprotected driver. this is because the airbag
increases the time interval over which the impulse is experienced 9cm
a bullet moving horizontally strikes and sticks in a block of wood that is free to move on the horizontal, level, frictionless surface. the block has a much greater mass than the bullet. what becomes of most of the momentum of the bullet
it becomes total momentum of the block plus the bullet 9cm
bucket hangs into a well from a rope. the rope is wound on a spool of radius r. as the bucket is brought up the rope wraps around the spool, increasing the radius at which the rope winds. if the spool is rotated at a constant angular speed, what happens to the speed of the bucket as it comes up?
it increases ( The speed of the rope on the spool is w r, so if r increases and w remains constant, the speed must increase.) 10cm
a rocket blasts off from earth on its way to the moon. as the rocket travels, it loses mass burning fuel and ejecting stages of the rocket. when the mass of the rocket has been reduced to one-half of its original mass it has traveled a distance equal to the radius of the earth away from the surface of earth where it took off. at this point, how does the gravitational force between rocket and earth compare to the gravitational force at lift off?
it is 1/8 of what it was at lift off ( The mass has been reduced by a factor of two and the distance has been doubled. Using Newton's gravitation equation, we get a factor of one-half for the mass decrease and another factor of one-fourth for the distance being one-half and then being squared.) cm13
an object moving with constant speed in a circular path
must have a net inward force acting on it] cm6
acar is slowing down as it goes around a curve. the total acceleration of the car points in which direction?
partly towards the center of the curve and opposite to the direction of the car's velocity (The centripetal acceleration is always toward the center of the circle and the car is slowing down, so the tangential acceleration is opposite to the direction of the car.) cm4
suppose a special spring is made that has an unusual force law. the force law of this spring is F=-kx^3. the motion of mass attached to this spring will be
periodic motion, but not simple harmonic motion (You only get simple harmonic motion for Hooke's Law type forces, i.e. F = -kx. You get periodic motion with any kind of force law which is a restoring force that doesn't change in time.) cm14
as you drive your car down the road, you notice a rattle in one of the doors. you notice that it is worst at 35mph. when you are going either 25 or 45 it doesn't rattle much at all. this is most likely a consequence of
resonance (The speed dependence of the rattle is explained by resonance. When you are going slowly the car shakes the door too slowly to cause the rattle. When you are going fast the frequency is too high for the rattle. When you are going 35, the frequency is just right.) cm14
x component of given vector is equal to that vector magnitude multiplied by which function below given theta is the angle between the vector and the y axis?
sin theta (the sine function is the opposite over the hypotenuse, so given which angle is defined as theta, this is the correct choice) cm3
a body falls freely from rest, straight downward. it has a constant acceleration of 9.8. this means that the m/s2
speed of the body increases 9.8 m/s during each second that it falls cm2
a solid sphere A rolls down an inclined plane, while an identical sphere, B slides down the plane without friction. they start from the same height. which of the following happens?
sphere B arrives first ( For sphere A the potential energy gets partly converted into rotational kinetic energy, leaving less for the translational part of the kinetic energy, thus slowing it down. For sphere B it all becomes translational kinetic energy. Thus B arrives before A.) cm10
it is past midnight and sue is sliding down the rope from her third floor window. as she slides down the rope faster and faster she tightens her grip on the rope. thus the force between her hand and the rope gradually increases. when it becomes equal to sue's weight
sue will continue downward at a constant speed (There are two forces acting on Sue, her weight and the force of the rope on her hand. When they are equal she will then have no acceleration. This means that she will move with a constant speed.) cm5
a rock is thrown upward from the top of a tower. it rises at first and eventually falls to the ground at the base of the tower. at what point in its motion is its acceleration least?
the acceleration is the same at all points in the motion of the rock cm2
you are riding passenger seat of car as it goes around a tight turn. you slide across seat to the passenger side door. which statement describes what is happening?
the car seat exerts a centripetal force on you but not enough to keep you in place so the door exerts the rest (friction between yourself and the seat is centripetal force that the car exerts on you. if friction is not large enough, you slide outward until you run into a door that exerts the rest of the centripetal force necessary to bring you around the corner with the car) cm6
subtract 430.1 from 431.2 then multiply the result by 472.6, what determines the limit for sig fi
the fact that we subtract 430.1 from 431.2 cm1
the amplitude of a simple harmonic oscillator is doubled.which of the following remain the same?
the frequency (The frequency depends only on the spring constant and the mass, not the amplitude.) cm14
a rocket fully loaded with fuel is fully loaded with fuel is sitting in space far from any other body. the engine is started and the rockets starts to spew exhaust gases out of the back of the engine. which of the following explains what happens?
the momentum of the exhaust gases must be equal to the momentum gained by the rocket. 9cm
consider a bicycle parked on a hill and pick the axis of rotation to pass through the point where the front tire touches the ground. the weight of the bicycle exerts a torque about this axis. what other forces on the bicycle will also exert a torque about this axis?
the normal force on the back wheel only cm12
elevator is moving downward with constant speed. ball is hanging from string of roof. the reaction force to the weight of the ball is
the pull of the ball upward on the earth (The weight of the ball is the pull of the Earth downward on the ball. To get the Newton's third law force, just reverse the object exerting the force and the object affected, so in this case it is the pull of the ball upward on the Earth.) cm5
for three vectors to add up to zero, what must be true of the magnitude of the three vectors?
the sum of two magnitudes must be greater than or equal to the third for all three vectors cm3
A small but massive block sits on top of another block as indicated in the diagram. The lower block sits on the floor. The coefficient of static friction is the same for the surface between the lower block and the floor and the surface between the upper and lower block. The upper block has twice the mass of the lower block, but the lower block is twice as long as the upper block. A horizontal force, F, is applied to the upper block, as shown in the diagram. The force is gradually increased from zero until something happens. Which of the following will happen first?
the upper block will start to slide along its contact surface with the lower block (The normal force between the two blocks is 2mg, so the maximum static frictional force between the two blocks is 2m mg. The normal force between the lower block and the floor has to be 3mg, so the maximum static frictional force between the lower block and the floor is 3m mg. Therefore the upper block will give way first.) cm5
three forces act on an object which is moving in the x direction with constant velocity. which of the following is true?
the vector sum of two of the forces must be equal to the negative of the third (If the vector sum of two of the forces equals the negative of the third, then they all sum to zero. That implies an acceleration of zero, and therefore a constant velocity, which is what we have here.) cm5
an airline pilot flies on a straight course, relative to ground from city a due east to city b. there is wind directly from the north, perpendicular to the desired path of the plane. what is the effect of this wind? assume airspeed is same with and without wind
the wind hinders hi, , so that the trip takes more time than if there was no (In order to fly due east relative to the ground, he now needs to compensate for the wind by aiming his plane somewhat to the north. This reduces the eastward component of his velocity, which makes it take longer for him to reach his destination.) cm4
ball is falling through air. it has two forces acting on it, its weight and air resistance. which is true?
there are both conservative and nonconservative forces acting on ball (Air resistance is nonconservative, Gravity is conservative.) cm7
pendulum a has a mass of 100g and pendulum b has a mass of 250 g. they have the same length. the pendulum with the longest period would be
they will have the same period. (The period of a pendulum doesn't depend on its mass, just the length of the string and the acceleration of gravity.) cm14
block A is traveling due north with a velocity of 10m/s. block B is traveling due east with a velocity of 1m/s. block A has 10 times the mass of block B. the two blocks stick together after the collision. after the collision the two blocks
travel slightly east of north 9cm
constant acceleration. we had an object with an acceleration that increased linearly with time, a(t)= a0t. which of the equations below is not one of the equations of motion for this case?
vf2^2= vi^2 + 2a0(dx) cm2
an artificial earth satellite is in an elliptical orbit with the earth at one focus. it has the greatest speed
when it is nearest the earth ( By Kepler's second law it sweeps out equal areas in equal times. When it is closest to the Earth the radius is smallest, so the speed it travels must be greatest.) cm13
a body falling through the air reaches a constant maximum speed
when the air resistance equals its weight (A body reaches constant speed when the forces on it balance. The only two forces acting on this body are the air resistance and its weight.) cm6
in solving a torque balancing homework problem for a beam in static equilibrium, where must we put the axis of rotation?
wherever we want to cm12
A box is pushed across the floor against a constant frictional force. The box is pushed across the room to the east in 30 seconds and returned to its starting point (pushed to the west) in 60 seconds. Which of the following is true about the work done and the power expended in both directions?
work going east= work going west; power going east> power going west (n both cases (east and west) the average force applied to the box is equal to the frictional force (because there is not net change in Kinetic Energy.) This means that the work (force times distance) is the same in both directions. Power is the rate of doing work, and it takes more time to move to the west, so there is more power expended going east (P=W/t).) cm8
which of the equations below is in error, as shown by dimensional analysis?
x= not + at/2 cm1
