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If v =<2,−3,5>m/s, what is | -1/2v |?

3.08m/s

What is the magnitude of the vector <3,5,−2>? a.5.48 b. 6.16 c. 6.00 d. 30.00 e. 38.00

B To find the magnitude of r =<rx,ry,rz> use r=|r|=√rx^2+ry^2+rz^2.

A 56g tennis ball is moving with a velocity of <0,0,−12> m/s when it collides with a wall. It rebounds with a velocity of <0,0,10> m/s. What is the change in the ball's momentum from just before to just after the collision with the wall? a. <0,0,22> kg m/s b. <0,0,−22> kg m/s c. <0,0,1.23> kg m/s d. <0,0,−1.23> kg m/s e. <0,0,0.112> kgm/s f. <0,0,−0.112>kgm/s

C Compute the change in momentum using Δp= pf−pi = m(vf−vi)

A yo‐yo is in the xy plane. You pull up on the string. What is the direction of the torque you exert on the yo‐yo? +x -x +y -y +z -z zero magnitude

+z Apply the right hand rule to r × F goes from the center of the circle to point of attachment of F (x-dir) F points upward (in y-dir)

Moving objects left the traces A, B, C, and D as shown. The dots were laid down at equal time intervals. Which objects did NOT interact with another object somewhere?

-If the object does not interact with any other object then it must move at constant velocity. -Motion with constant velocity would be described on the motion diagram by equally spaced dots in a straight line.

What is the direction of < 0, 0, 3 > × < 0, 4, 0 >? +x -x +y -y +z -z zero magnitude

-x z^×y^=−x^

Consider an electron (mass 9 x 10^-31 kg) moving with speed v = 0.9c. What is its rest energy? a. 7.30 x 10-31 J b. 8.10 x 10-14 J c. 1.05 x 10-13 J d. 1.86 x 10-13 J e. 2.87 x 108 m/s

B Calculate the rest energy using mc^2. The actual velocity of the electron doesn't factor into the rest energy.

A ball bounces off a wall. mass 0.1 kg vi = 6 m/s vf = 6 m/s What is the change in px of the ball? a. 0 kg m/s b. -1.2 kg m/s c. +1.2 kg m/s d. +0.6 kg m/s e. -0.6 kg m/s

B Δpx=pxf−pxi =mvfx−mvfi =(0.1kg)(−6m/s)−(0.1kg)(+6m/s) =-1.2 kg m/s

A ball whose mass is 2 kg travels at a velocity of <0,-3,4>m/s. What is the rest energy of the ball? a. 0J b. 25J c. 6.0x10^8J d. 9.3x10^16J e. 1.8x10^17J

E Rest energy is calculated using mc^2, where c=3×10^8 m/s is the speed of light.

What is the direction of < 0, 0, 6 > × < 0, 0, -3 >? +x -x +y -y +z -z zero magnitude

0 z^×z^=0

You have a pot containing 1000 grams of water over a fire, and you are also stirring the water with a paddle. Take the water as the system. Because the fire is at a higher temperature than the water, there is an energy transfer due to a temperature difference of Q = 5000 J to the water from the fire. At the same time, there is external work W = 2000 J done by you on the water.What is the increase in the thermal energy of the water?

7000 J ΔEThermal=Q+W

The spokes of a bicycle wheel have low mass, so almost all of the mass of the wheel is concentrated in the rim. What is the moment of inertia of a bicycle wheel of radius R and mass M? a. MR^2 b. 2πMR^2 c. 2πRM d. 1/2MR^2 e. πMR^2

A All of the mass is a distance R from the axis of rotation.

A hockey puck is sliding along the ice with nearly constant momentum <10,0,5> kg m/s when it is suddenly struck by a hockey stick with a force <0,0,2000> N that lasts for only 3 ms (3×10^‐3 s). What is the momentum of the puck after the impact? a. <10,0,11> kg∙m/s b. <0,0,6> kg∙m/s c. 14.86 kg∙m/s d. <16,0,11> kg∙m/s e. <0,0,30> kg∙m/s

A Compute the final momentum using pf=pi+Fnet Δt - You can also notice that the force has only a z-component so the only the z-component of momentum will change.

The relative position vector from the star to the planet is <1.5×10^11,0.5×10^11,0> m. The distance between the star and the planet is 1.58×10^11 m. What is the unit vector r^? a. <0.949,0.316,0> b. <0.447,0.894,0> c. <0.800,0.600,0> d. <1,0,0> e. <1,1,0>

A Compute the unit vector by dividing the vector by its magnitude

After the collision, what is the speed (in m/s) of the child? a. ωR b. ω c. ωR2 d. ω/R e. ω2R

A Since the child is a distance R from the axis of rotation, its speed will be given by v=ωR

A fancart moves in the -x direction. The fan is on, and the force on the cart by the air is also in the -x direction.Is the work done by the air positive, negative, or zero? a. Positive b. Negative c. Zero

A The cart will speed up and the kinetic energy will increase, so the work done is positive.

A spring whose stiffness is 30 N/m is 12 cm (0.12 m) long when relaxed. You push on the spring, compressing it so its length is now 10 cm (0.10 m). What is the magnitude of the force the spring now exerts on your hand? a. 0.6N b. 3N c. 3.6N d. 30N

A The magnitude of the force exerted by the spring will be given by |F|=k|s|where k is the force constant of the spring.

Tarzan swings from a vine. At the bottom of the swing, how does the magnitude of the force by the vine on Tarzan compare to the force by the Earth on Tarzan? a. Fvine>FEarth b. Fvine=FEarth c. Fvine<FEarth not enough information

A The net force is in the position y-direction. The only forces in the y-direction are tension and gravitational. The tension force is in the position y-direction, which means it must be greater than the gravitational force in the negative y-direction to have a net force in the position y-direction.

A hydrogen atom is initially in the excited state N = 4. It emits a photon and ends up in the state N=2. What is the energy of the emitted photon? A.E4-E2 B. E2-E4 C. E4 D. E2 E. |E4| F. |E2|

A The photon energy is the difference between the final and initial energy levels.

An alpha particle contains two protons and two neutrons, and has a net charge of +2e. The alpha particle is 0.1 m away from a single proton, which has charge +e. Which statement about the magnitudes of the electric forces between the particles is correct? a. The force on the proton by the alpha particle is equal to the force on the alpha particle by the proton. b. The force on the proton by the alpha particle is larger than the force on the alpha particle by the proton . c. The force on the proton by the alpha particle is smaller than the force on the alpha particle by the proton.

A These forces are equal in magnitude and opposite in direction by Newton's Third Law.

A spaceship far from all other objects uses its rockets to attain a speed of 1×1041×104 m/s. The crew then shuts off the power. According to Newton's first law, which of the following statements about the motion of the spaceship after the power is shut off are correct? A. The spaceship will move in a straight line. B. The spaceship will travel on a curving path. C. The spaceship will enter a circular orbit. D. The speed of the spaceship will not change. E. The spaceship will gradually slow down. F. The spaceship will stop suddenly.

A and D Newton's First Law predicts that once the power is shut off that the velocity of the space ship will remain constant.

Which of the following do you see moving with constant velocity? A. A ship sailing northeast at a speed of 5 meters per second The Moon orbiting the Earth B. A tennis ball traveling across the court after having been hit by a tennis racket C. A can of soda sitting on a table D. A person riding on a Ferris wheel that is turning at a constant rate.

A and D Remember that velocity is a vector and has both magnitude and direction. If an object is moving in a curved path then its direction is changing so its velocity is not constant. Also, at object at rest has a constant velocity of zero.

In which of the following situations is there observational evidence for significant interaction between two objects? A.A ball bounces off a wall with no change in speed. B .A baseball that was hit by a batter flies toward the outfield. C. A communications satellite orbits the Earth. D. A space probe travels at constant speed toward a distant star. E. A charged particle leaves a curving track in a particle detector.

A, B, C, and E (a) The velocity of the ball will change when it hits the wall because its direction changes. (b) Gravity will cause the vertical velocity of the ball to change. (c) The gravitational interaction between the satellite and the Earth it what keeps the satellite in orbit. (e) The curved track left in the particle detector indicates that something interacted with the charged particle causing its velocity to change.

Fixed star position: rs=<0.5×10^11,1×10^11,0>m Initial planet position: rp=<2×10^11,1.5×10^11,0>m What is the vector that points from the star to the planet ? a. <1×10^22,1.5×10^22,0> m b. <1.5×10^11,0.5×10^11,0> m c. <‐1.5×10^11,‐0.5×10^11,0> m d. <2.5×10^11,2.0×10^11,0> m e. Not enough information given

B A vector that points from the start to the planet will be given by r =rp−rs

In a spring‐mass oscillator, when is the magnitude of momentum of the mass largest? a. When the magnitude of the net force acting on the mass is largest. b. When the magnitude of the net force acting on the mass is smallest. c. At some other time.

B At the extremes of the motion (when the spring is stretched the farthest or compressed the most) the force on the mass is the largest, but the object is at a velocity of near zero. It is turning around at these points. On the other hand, the object will be moving the fastest (and thus have the largest momentum magnitude) when it is moving through its equilibrium position of the motion where the force is zero (when the spring isn't compressed or stretched).

skater on a skateboard moves 0.5 m in the +x direction while his friend is pushing on him with a force of 10 N in the −x direction, slowing him down. The amount of work his friend does on him is: a. +5J b. -5J c. 0J d. None of the above

B Calculate the work using W=F dot Δr

A proton is at location <0,3,−2> m.An electron is at location <−1,0,−6> m. What is the relative position vector from the proton to the electron? a. <−1,3,−8> m b. <−1,−3,−4> m c. <1,3,4> m d. <1,−3,8> m e. <1,0,6> m

B Compute r =re−rp

he disk has moment of inertia I, and after the collision it is rotating with angular speed ω. The rotational angular momentum of the disk alone (not counting the child) is a.<0,0,0> b. <0,-Iω,0> c. <0,Iω,0> d. <0,0,-Iω> e. <0,0,Iω>

B Find the magnitude of the angular momentum using L=Iω and then use the right-hand rule to find the direction.

What is the initial angular momentum of the child + disk about the axle? a. <0,0,0> b. <0,-Rmv,0> c. <0,Rmv,0> d. <0,0,-Rmv> e. <0,0,Rmv>

B Find the magnitude using L=r⊥pL=r⊥p, then use the right hand rule to show that the direction is downward, in the −y^ direction.

Two balls, each of mass 0.7 kg, are connected by a low (negligible) mass rigid rod of length 0.4 m. The object rotates around a pivot at its center, with angular speed 13 radians/s. What is the rotational kinetic energy of this object? a. 484J b. 4.73 J c. 2.37 J d. 0.056 J e. 0J

B I=mR^2+mR^2 K=1/2*I*ω^2 =1/2(2mR^2)ω^2 =mR^2ω^2

If the Mars rover measured the value of g on Mars, it would be: a. 9.8 N/kg b. Less than 9.8 N/kg c. Greater than 9.8 N/kg

B Mars' smaller mass reduces the value of g by about a factor of 1/10. However, it's smaller radius (~ 1/2 rEarth) increases the value by nearly a factor of 4. The combined effect is a reduction of approximately 4/10.

Suppose the period of a spring‐mass oscillator is 1 s. What will be the period if we double the spring stiffness? a. 0.5s b. 0.7s c. 1.0s d. 1.4s e. 2.0s Note: To double the stiffness we could use a stiffer spring, or we could attach the mass to two springs.

B Since the period of a mass spring system is given by T=2π*sqrt(m/k) doubling the stiffness will cause the period to change by a factor of 1/√2.

The soccer coach tells you that when the ball rolls by you should kick it in the new direction you want it to go. What are the correct instructions? a. The coach is right. b. pfuture is determined not only by the impulse but also by pnow, so that won't work. c. You have to kick perpendicular to the motion to change the direction. d. You have to stop the ball before you can make it go in a different direction.

B The new direction of motion for an object is dependent on the direction of impulse and the current direction of momentum.

A child runs and jumps on playground merry‐go‐ round. For the system of the child + disk (excluding the axle and the Earth), which statement is true from just before to just after impact? a. K,P and L do not change. b. P and do not change c. L does not change. d. K and P do not change. e. K and L do not change.

B This is essentially a completely inelastic collision. Both linear and angular momenta will be conserved as they are in any collision. Since this is inelastic, kinetic energy will not be conserved.

A tennis ball traveling 50 m/s bounces off a wall. Estimate the time during which the ball is in contact with the wall. a. 0.00001 s b. 0.001 s c. 0.1s d. 1s

B You can make an estimate of the duration of the collision using Δx=vavgΔt You will need to make an estimate for how far Δx the ball might compress during the collision. The average velocity of the ball can be found from (50+0)/2 m/s.

A yo‐yo is in the xy plane. You pull up on the string with a force of magnitude 0.6 N. What is the magnitude of the torque you exert? r = 0.005 mR= 0.035 m a. 0.005 N∙m b. 0.003 N∙m c. 0.021 N∙m d. 0.035 N∙m e. 0.6 N∙m f. cannot be determined without knowing the length of the string

B τ= rt * F= (0.005m)(0.6N)=0.003Nm

An isolated neutron decays: n→p + e + v Initial state: neutron at rest Final state: p+, e− ,v far from each other Which statement is correct? a. The sum of the rest energies of the products equals the rest energy of the neutron. b. The sum of the kinetic energies of the products equals the rest energy of the neutron. c. The sum of the rest energies and kinetic energies of the products equals the rest energy of the neutron. d. The sum of the kinetic energies of the products equals the kinetic energy of the neutron.

C

Which of the following statements is correct? Q and ∆Ethermal are the same thing. Q and ∆Ethermal are not the same thing, but they are always equal. ∆Ethermal can be nonzero even if Q is zero. Q and ∆Ethermal are both always positive.

C

As a comet travels away from a star, how do the kinetic energy K and potential energy U of the comet + star system change? a. K:increase U: decrease b. K:increase U:increase c. K:decrease U:increase d. K:decrease U:decrease e. K:no change U:no change

C As the comet travels away from the star it will slow down, losing kinetic energy. This loss will be offset by and increase in potential energy.

Distance from the star to the planet: r=1.58×10^11m Star's mass: ms=1×10^30 kg Planet's mass: mp=5×10^24 kg G=6.7×10^−11N∙m2/kg2 What is the magnitude of the gravitational force that the star exerts on the planet? 1.34×10^−8 N 2.68×10^−2 N 1.34×10^22 N 2.12×10^33 N 5.30×10^55 N

C Evaluate the magnitude of the gravitational force using Fgrav on 2 by 1=G* (m1m2)/r^2

You push an initially stationary 100 kg mass on the floor with a horizontal force. The coefficient of static friction is 0.6. What is the magnitude of the minimum force you need to exert on the mass in order to get it to move horizontally? a. 980 N b. 667 N c. 588 N d. 400 N Not enough information

C If the mass is on the verge of slipping then its momentum will be constant (actually zero). It's momentum change will of course also be zero. When we apply the momentum principle in the vertical direction we will find that the normal force equals the weight mg of the mass (in this case). When we apply the momentum principle in the horizontal direction, and use the fact that fs=μs*FN=μs*mg since the mass is on the verge of slippling, we find that the applied force must be the same as this friction force or μs*mg = 588 N.

The mass of one atom is mm (kg/atom). The density of solid copper is ρ (rho) (kg/m3). What is the volume occupied by one atom of copper in a solid? a. mρ b. ρ/m c. m/ρ d. ρ3m

C Simply start with the definition of density (mass/volume), ρ=m/V, and solve for the volume. Another approach here would be to use dimensional analysis and make sure that the result that you choose has units of volume (m3), or in this case since you are looking for the volume of one atom it will be in m3/atom.

How does the diameter of one atom in a solid compare to the length of an interatomic bond? a. The bond length is greater than the atomic diameter b. The bond length is less than the atomic diameter c. They are equal

C The length of an inter-atomic bond in a solid is defined as the center-to-center distance between the pair of atoms. This is the same as the diameter of an atom, including the full electron cloud.

suppose the period of a spring‐mass oscillator is 1 s with an amplitude of 5 cm. What will be the period if we increase the amplitude to 10 cm, so that the total distance traveled in one period is twice as large? a. 0.5s b. 0.7s c. 1.0s d. 1.4s e. 2.0s

C The period of a simple harmonic oscillator (mass-spring system) is independent of the amplitude of the motion.

You hold a tennis ball at rest above your head, then open your hand and release the ball, which begins to fall. At this moment, which statement about the magnitudes of the gravitational forces between the Earth and ball is correct? a. The force on the ball by the Earth is larger than the force on the Earth by the ball. b. The force on the ball by the Earth is smaller than the force on the Earth by the ball. c. The force on the ball by the Earth is equal to the force on the Earth by the ball.

C These forces are equal in magnitude and opposite and direction by Newton's Third Law. When the ball is released, the only force acting on it will be the gravitational force by the Earth. As a result, the ball will experience a net unbalanced force and will it's momentum will begin to change (it will accelerate toward the surface of the Earth).

The mass of the Sun (2×10^30kg) is much larger than the mass of the Earth (6×10^24kg). If F on Sun is the magnitude of the force on the Sun by the Earth, and F on Earth is the magnitude of the force on the Earth by the Sun, which of the following is true? a. F on Sun>F on Earth b. F on Sun<F on Earth c. F on Sun=F on Earth

C These forces are equal in magnitude and opposite in direction by Newton's Third Law.

The relative position vector from the star to the planet is <1.5×10^11,0.5×10^11,0> m. What is the distance between the star and the planet? a.0.53×10^11 m b. 1.00×10^11 m c. 1.58×10^11 m d. 2.00×10^11 m e. 2.36×10^11 m

C r=|r| is simply the magnitude of r

Which of the following is a property of all "elastic" collisions? a. The colliding objects interact through springs. b. The kinetic energy of one of the objects doesn't change. c. The total kinetic energy is constant at all times — before, during, and after the collision. d. The total kinetic energy after the collision is equal to the total kinetic energy before the collision. e. The elastic spring energy after the collision is greater than the elastic spring energy before the collision.

C and D In an elastic collision no kinetic energy is converted to internal energy. K will be constant.

A diatomic molecule such as molecular nitrogen (N2) consists of two atoms each of mass M, whose nuclei are a distance d apart.What is the moment of inertia of the molecule about its center of mass?

C, 1/2 Md^2 I=M(d/2)^2+M(d/2)^2= 1/2 Md^2

What is the unit vector in the direction of the vector <3,5,−2>? a. <3,5,−2> b.<1,1,−1> c. <0.49,0.81,0.32> d. <0.49,0.81,−0.32> e. <0.3,0.5,−0.2>

D

Consider an electron (mass 9 x 10^-31 kg) moving with speed v = 0.9c. What is its total particle energy? a. 7.30 x 10-31 J b. 8.10 x 10-14 J c. 1.05 x 10-13 J d. 1.86 x 10-13 J e. 2.87 x 108 m/s

D Calculate the total particle energy as E=γmc^2

During a particular time interval the average velocity of a 56g tennis ball is <5,−3,−2> m/s. What is the unit vector in the direction of the ball's average momentum? a. <0.280,−0.168,−0.112> b. <0.829,−0.518,−0.207> c. <1.44,−0.866,−0.577> d. <0.811,−0.487,−0.324> e. <−0.873,−0.436,−0.218>

D First find the momentum p=mv and then find a unit vector in the direction of p by dividing the momentum vector by its magnitude

Tarzan's mass: 100 kg. Length of vine: 5 m. Tarzan's speed: 13 m/s. What is the tension in the vine at this instant? a. 980 N b. 3380 N c. 2400 N d. 4360 N

D In the y-direction: Fnet=mg+mv^2/r

A sodium ion exerts a force of 3×10^-8 N on a proton that is a distance d away. If the sodium ion were moved to a distance 3d from the proton, what would the magnitude of the force on the proton be? a. 9×10^-8N b. 3×10^-8 N c. 1×10^-8N d. 0.33×10^-8N e. 0.11×10^-8 N

D Increasing the separation from dd to 3d will reduce the force by a factor of 1/3^2=1/9

The gravitational force exerted by a planet on one of its moons is 3×10^23N when the moon is at a particular location. If the mass of the moon were 3 times as large, what would be the force on the moon? a.1×10^23N b. 3×10^23 N c. 6×10^23 N d. 9×10^23N

D Recall the gravitational force is given by Fgrav on 2 by 1=−G*(m1m2)/r^2 so if m1 increases by a factor of 3 then so will the gravitational force.

Suppose the period of a spring‐mass oscillator is 1 s. What will be the period if we double the mass? a. 0.5s b. 0.7s c. 1.0s d. 1.4s e. 2.0s

D Since the period of a mass spring system is given by T=2π*sqrt(m/k) doubling the mass will cause the period to increase by a factor of √2.

A ping‐pong ball bounces elastically off a bowling ball which is initially at rest. After the collision the ping‐ pong ball's kinetic energy is Kp. What is the kinetic energy of the bowling ball? a. Kp b. -Kp c. much greater than Kp d. negligibly small (nearly zero)

D The bowling ball is very massive. Its final velocity will be very small.

An ideal mass‐spring system is oscillating with angular frequency ω=sqrt(ks/m). More energy is put into the mass‐spring system. What is now true? a.The frequency of the oscillations increases. b.The frequency of the oscillations decreases. c. The frequency increases and amplitude increases. d. The frequency is unchanged and the amplitude increases. e.The frequency decreases and amplitude decreases.

D The frequency only depends on the strength of the spring and the mass of the oscillator.

A horizontal spring has a mass attached which can move with negligible friction. You stretch the spring and release the mass from rest. For the resulting motion, which of the following statements is TRUE? A. When the spring is (momentarily) fully compressed, K has its largest value. B. When the spring (momentarily) has its relaxed length, U has its largest value. C. When the spring (momentarily) has its relaxed length, K has its smallest value. D. When K is large, U is small, and vice versa. E. When K is large, U is large, and vice versa.

D The fully compressed position of the spring is a turning point of the motion, where v=0, k=0, and U is maximum. The relaxed position of the spring F=0, U is minimum and K is a maximum.

A block with mass m = 0.5 kg is attached to a horizontal spring with stiffness ks= 40 N/m and relaxed length L0= 0.16 m. The current length of spring is L = 0.12 m and the current velocity of block is <-0.30,0,0> m/s. What is the momentum of the block at a time 0.02 seconds later? a. <1.45,0,0> kg∙m/s b. <-0.268,0,0> kg∙m/s c. <-0.236,0,0> kg∙m/s d. <-0.118,0,0> kg∙m/s e. <-0.182,0,0> kg∙m/s Friction is negligible. Approximate the force as constant over this time interval.

D Use the momentum prinicple to find the new momentum. pf=pi+ FsΔt= mvi − ks Δt Be careful when computing the stretch s =L−L0

you push a 100 kg mass on the floor with a horizontal force of 400 N. It doesn't move. The coefficient of static friction is 0.6. What is the magnitude of the frictional force on the block by the floor? a.980 N b 667 N c. 588 N d. 400 N Not enough information

D We are told that despite pushing with a force of 400 N on the mass that it doesn't move. Evidently the mass is in equilibrium. The net force on it is zero. The frictional force must be providing a force to exactly oppose the applied force of 400 N. If we increase our applied horizontal force a little both then the friction force will also increase. A good question to think about is how large can the applied force be before the mass will start to move?

The gravitational force exerted by a planet on one of its moons is 3×10^23N when the moon is at a particular location. If the distance between the planet and the moon were doubled, what would be the force on the moon? a. 6×10^23 N b. 3×10^23N c. 1.5×10^23N d. 0.75×10^23N e. 0.33×10^23N

D If the separation distance, which shows up squared and in the denominator of the gravitational force law, is doubled then the force will decrease by a factor of 1/4.

A 0.4 kg mass connected to a low mass horizontal spring of stiffness 200 N/m slides on a very low friction surface. You observe the system at a moment when the spring is compressed 10 cm and the speed of the mass is 3 m/s. What will the kinetic energy of the mass be when the spring is stretched 5 cm?

E K1+U1=K2+U2 1/2m(v1)^2+12k(Δx1)^2=K2+1/2k(Δx2)^2 1/2(0.4kg)(3m/s)^2+1/2(200N/m)(−0.10m)^2=K2

Imagine an atom which only has two electronic energy levels. The ground state energy is -3.0 eV, and the excited state has an energy of -1.1 eV. A sample containing many such atoms is irradiated with visible light that contains photons of all energies from 1.8 eV up to 3.1 eV. What are the energies of the photons that are absorbed, and therefore are not detected in the outgoing light beam? The detector will detect photons of all energies - none are missing. A. 1.1 eV B. 3.0 eV and 1.1 eV C. 3.0 eV D. 1.9 eV

E The absorbed energy in the spectrum corresponds to the energy difference between the initial and final levels in the atom.

The magnitude of the force that the star exerts on the planet is 1.34×10^22 N, and the unit vector that points from star to planet is <0.949,0.316,0> What is the force that the star exerts on the planet? a.<1×10^22,1.5×10^22,0> N b. <1.5×10^11,0.5×10^11,0>N c. <−1.5×10^11,−0.5×10^11,0> N d. <2.5×10^11,2.0×10^11,0> N e. <−1.27×10^22,−4.24×10^21,0> N

E The force on the planet by the star is given by Fon planet by star=Fon planet by star(−rhat)

A ball whose mass is 2 kg travels at a velocity of <0,-3,4> m/s.What is the kinetic energy of the ball? a.<0,-6,8> b. 0J c. 2J d. 10J e. 25J

E The kinetic energy is calculated using K=1/2 mv^2

A bee flies in a straight line at constant speed. At 15 s after 9 AM, the bee's position is <2,4,0> m. At 15.5 s after 9 AM, the bee's position is <3,3.5,0> m. What is the average velocity of the bee? a. <6,7,0> m/s b. <0.193,0.225,0> m/s c. 2.236 m/s d. <0.500,−0.250,0> m/s e. <2.000,−1.000,0> m/s

E To compute the average velocity use v =Δr/Δt

Lead (Pb) atoms are much heavier than aluminum (Al) atoms, with atomic masses of about 207 g/mol for Pb and 27 g/mol for Al. Interatomic bond strengths are also much weaker in Pb (5 N/m) than in Al (16 N/m). Which vibrational energy level diagram below represents Pb, and which represents Al?

PICTURE NOT SHOWN, BUT Energy level differences are proportional to angular frequency, which is equal to sqrt(k/m). Thus for comparable atomic mass, larger energy level differences result from higher interatomic bond stiffness. heaver= larger curve, not as steep

Two lead bricks moving in the +x and −x directions, each with kinetic energy K, smash into each other and come to a stop.What happened to the energy?

The kinetic energy changed into thermal energy.

A particle travels at constant speed along the path shown at left. When the particle is at location C, which green arrow best indicates the direction of dp/ dt?

Towards the direction of the inside of the kissing circle!

Which of the following graphs of U vs r represents the gravitational potential energy, U = -GMm/r?

U approaches -infinity as r approaches zero, and it approaches zero as r approaches infinity.

Suppose the period of a spring‐mass oscillator is 1 s. What will be the period if we cut the spring in half and use just one of the pieces? a. 0.5s b. 0.7s c. 1.0s d. 1.4s e. 2.0s

When you cut the spring in half and only use one piece you are making a the spring be stiffer. In fact, the stiffness will double. Since the period of a mass spring system is given by T=2π*sqrt(m/k) doubling the stiffness will cause the period to change by a factor of 1/√2.

A feather falls toward the ground at constant speed. Which is the direction of the net force on the feather during one time step? a. Downward b. Upward c. The net force is zero (no direction)

c. The feather is moving with constant speed and its direction of motion is not changing. Thus, its velocity and momentum are constant. The momentum principle implies that the net force on the feather must be zero for the momentum to remain consant. The downward gravitational force is apparently exactly cancelled by an upward air drag (friction) force.

Which of these arrows represents the vector <−4,2,0>

no picture, but The vector <−4,2,0> is described by a change in four units to the left (-x) and two units up (+y).

spacecraft moves from point A to point B along the path shown below. Which green arrow best indicates the direction of the spacecraft's average velocity from point A to point B?

picture not shown, but The average velocity is the displacement per unit time. The displacement vector will point from the initial position (A) to the final position (B).