C/P Uworld missed q's 3/8/23

Q20. At its top speed, a Mars rover generates a constant force of 400 N and uses 100 W of battery power. What is the top speed of the rover? a) 2.5 m/s b) 1.0 m/s c) 0.25 m/s d) 0.10 m/s

must be the silliest mistake I ever did see cuz Im pretty sure I knew the formula too, so many a little math error? Its just Power formula: P = W/t = F*d/t = F*v We have force and Power, solve for velocity bam done, its 0.25 m/s

Q36. Which of the following spherical mirrors produces a virtual image from the given light rays and has the larger radius of curvature? (Note: Assume that the distance between the object and mirror is greater than the focal length.) answer options were 4 pics of diff lens diagrams a) concave lens with a smaller focal distance b) concave lens with a larger focal distance c) convex lens with a smaller focal distance d) convex lens with a larger focal distance

obviously I immediately freaked seeing stuff about lenses *shudders* . but no need to fear All I had to know to get this right was firstly: - concave lens is one that is "caving" in towards you like this: ) -the convex lens is "vexxed with you" and turns its back to you and is facing this way: ( then had to know that concave lens will form a real image (in front of the lens), and convex lens will form a virtual image (behind the lens) after knowing concave vs convex lens and where the image forms, its just a matter of identifying which will have a greater radius of curvature; that means if we completed the circle using the focal point as the center, which would result in a larger circle? (i.e. looking for which one has a larger focal distance) ((also note every time ive said focal distance here and in the q I think I mean to say focal length.. lol))

P41. A 10 kg sled is pulled on level snow at an average speed of 0.5 m/s. What is the average power required to pull the sled? a) 10 W b) 20 W c) 40 W d) 50 W

ok so this question was a lil more ~complicated~ that it first appeared. Yes, P= F*v. however, this passage gave us info about friction forces / coefficients and all that jazz.. so its not as simple as that formula..! and i didnt know that at first, so was lost. basically, P = F*v is the starting but, bc friction is involved here, we're looking for a *frictional force* , which has the formula: F(friction) = mu(friction)*F(N) , the frictional coefficient times the normal force F(N) = mg the next challenge here is to think: but what is the F(friction) for us in this situation!? we weren't given mu(friction) for snow :( I just had to realize that the table of F(friction) values actually show me a pattern bw mass of the object and the friction force on the sled (N). the mass * 2 = frictional force so, the mass of 10kg sled * 2 = 20N must be my frictional force P = F*v P= 20* 0.5 P=10 W (option A)

Q33. A way to increase the transfer of heat from the body to the environment would be to: a) increase respiration rate b) increase residual volume of the lungs c) decrease alveolar surface d) decrease the blood flow in pulmonary vessels

I wasn't really sure about this one tbh.. I thought maybe heat has to do with constriction of blood flow? totally off/guessing. for this I had to know that heat is transferred out of the body and to the enviro by either conduction, convection (movement of a medium like blood or air to move the heat), or radiation. so convection is the mode of heat transfer in this situation (air going out of the lungs and into the enviro) that is relevant here. -pulmonary blood vessels can be *dilated* not constricted, to move heat out of the body -increasing respiratory rate would move more heat out of the body too , so option A

Q13. Which of the labeled intermolecular interactions in Figure 1 is the strongest dipole-dipole interaction between two covalent bonds?

again so tricky! bc I did pick the strongest interaction... it just wasn't a dipole-dipole interaction bc as previously stated, only I and II are dipole-dipoles smh so the strongest dipole dipole bw those is option II, because the H2O oxygen has a stronger partial negative charge than the oxygen in the C=O bond

Q 56. How will the work done by the Lorentz force on an electron traveling through the magnetic field of an MRI scanner change if the magnetic field strength is increased? a) The work will not change, because its always zero. b) The work will increase, bc the velocity of the electron will increase. c) The work will increase, bc the force on the electron will increase. d) The work will decrease, bc the velocity of the electron will decrease.

again this was Lorentz force, I had no clue what was happening so randomly guessed. but this is a little tricky anyway. I had to know that the relevant equation here is: W = F*d * cos(theta) We also know that F(magnetic) = qvBsin(theta) first you may think, oh well as the magnetic field B increases so will Force(magnetic)- maybe its option C! well this statement is not false... BUT. looking at the Work equation, the theta there is the angle between the directions of F and d. we know that the angle bw the Force(magnetic) and magnetic field is 90degrees, and that cos(90) = 0. So regardless of magnetic field increasing the magnetic force... the *work* done is zero, and always will be zero. (option A)

Q23. An astronaut pulls a cart of rock samples a distance of 60 m along flat ground using a tether attached to their spacesuit. The tether has a tension of 40 N and an angle of 30° relative to the horizontal. What is the approximate work the astronaut does on the cart? (Note: sin 30° = 0.50; cos 30° = 0.87) a) 1200 J b) 2000 J c) 2400 J d) 2800 J

almost had this... I knew something was not quite right w/ how I was approaching it considering they gave us all these #s for sins and cosines, which I didn't initially use but! its still p straightforward. I used W = F* d but I had to use W = F*d*cos(theta) which will yield W = (40)(60)(0.87) = 2000 J (option B)

Q54. Which of the following best describes the direction of the magnetic force on a positron traveling inside the magnetic field of an MRI scanner? (Note: Assume that the direction of the positron's velocity is not the same as the direction of the magnetic field.) a) It is in the same direction as the magnetic field b) It is perpendicular to the magnetic field c) It is in the same direction as positron velocity d) It is in the opposite direction as the positron velocity

blank stare at this one.. I hadn't studied Lorentz force or right hand rule so total guess here I just needed to know the right-hand rule, and the formula too, that relates the Magnetic Force, Magnetic Field, and Velocity of charged particle formula: F = qvBsin(theta) F is magnetic force q is charge of particle v is velocity B is the magnetic field theta is the angle bw the velocity and magnetic field bc this may not be 90 degrees. the angle bw the velocity and magnetic force will always be 90, and angle bw magnetic force and field will always be 90. but *angle bw velocity and field may not be 90* this info is what we use to answer the q. the magnetic force is gonna be perpedicular to the magnetic field, so option B is answer.

Q1. A spherical weather balloon is filled with helium gas with a density of about 0.18 g/L. If the diameter of the balloon is 20 m, what is the approximate mass of the helium in the balloon? (Note: The volume of a sphere is: answer: 750kg I mistakenly chose: 0.75 kg

clearly just a units/decimal mistake here!! watch the decimals and *be careful* a simple density = mass/ volume problem

Q48. Which of the following is NOT a characteristic of nearsighted vision? a) eye bends light too much b) corrected with a diverging lens c) corrected with a concave lens d) image forms behind the retina

correct answer is option D I didn't know lenses so i guessed randomly bro but! now I know CHAD nearsightedness and virgin farsightedness lmao made a review flashcard go review that

Q 58. A researcher wants to decrease the cutoff frequency of the RC filter circuit shown above by 50%. Would adding a 0.1 mF capacitor in series with the existing capacitor achieve the desired result? a) Yes, bc the equivalent capacitance would be 0.05 mF b) YEs, bc the equivalent capacitance would be 0.2 mF c) No, bc the equivalent capacitance would be 0.05 mF d) No, bc the equivalent capacitance would be 0.2 mF

for this I had to know the formula for cutoff frequency: f(c) = 1 / 2(pi)RC(eq) I also had to know that C(eq) is just the total capacitance when you have multiple capacitors. for Capacitors in series this means using the reciprocals (like as if its resistors in parallel) adding a 0.1mF capacitor would make the C(eq) equal to 0.05 overall equation logic: decreasing the denominator by half will double the f(c), not halve it, as the question asks. so the answer is C.

Q 52. A researcher uses a single slit diffraction pattern to evaluate a patient's vision. Which of the following changes will decrease the spacing of the diffraction pattern? a) decreasing the width of the slit b) decreasing the wavelength of the light c) increasing the wavelength of the light d) increasing the intensity of the light

for this q, I saw diffraction and freaked out bc haven't studied that yet but really boils down to understanding one formula: sin(theta) =m*λ / a which tells you the diffraction pattern of the *dark* bands --theta is the angle of the dark bands (higher theta basically indicates bands are further apart) --a is the width of the slit --λ is the wavelength of the light travelling thru the slit/doing this diffraction --m is any integer value question asks us which change would *decrease spacing of the diffraction pattern*, so we're looking for something that will decrease theta basically. sin(theta) is smallest/near 0 when theta is small/near 0. so now just look at our options; which would optimize equation to result in the smallest sin(theta) ? its gonna be B. decreasing the wavelength of the light ( λ )

Q28. What is the number of moles of gas exchanged in a single breath during normal breathing? (Note: Assume all gases are ideal and at STP.) a) 0.023 mol b) 0.045 mol c) 0.068 mol d) 0.11 mol

goofy math mistake!? girl pls. we are indian we dont make math mistakes.. but anywayyyys. it was an application of PV = NRT I did everything right, given all necessary info to solve for n (# of moles) even got the final division set up 0.5/21.6 ... then just did this calculation wrong lmao not cool

Q 59. According to the data in Table 1, which of the following makes noise at a frequency that resonates in the bore of an MRI magnet? (Note: The speed of sound in air is 350 m/s.) a) 1.0 T MRI b) 1.5T MRI c) 3.0 T MRI d) gas lawnmower

just needed to know the relevant formulas to get this one right so for an open pipe system like we have here (stated in passage), our formulas would be: wavelength = 2L/n frequency = nv/2L we will use the freq equation here, we know velocity 350m/s, L is 1.5m, and we're left with a ratio that will compare the frequency with n (essentially giving us the fundamental frequency here) anything that is a multiple of this fundamental frequency will resonate with the MRI magnet, which is what our q is asking we get: f = 140 n the 1.0T MRI machine has a freq of 700, which would totally resonate with this here! it would be the 5th harmonic, since n just has to be 5

Q2. Balloons can be used to carry loads upward in the air using buoyant force. A balloon of volume V = 14,000 m3 is filled with hydrogen gas of density ρh = 0.08376 kg/m3. The density of air is ρair = 1.204 kg/m3. Which expression gives the maximum possible mass of the load that can be lifted by the balloon? option A): (1.204-0.08376)*(14000) option B) (1.204-0.08376)* (14000) *(9.8) option D): (1.204+0.08376)*(14000)

kinda glanced thru options and picked this. did not know logically how to get here. So, I just needed to know the F(buoyancy) formula which is: Fb = p*g*V I then had to recognize all three forces acting on the balloon and what the heck is the situation here. so theres a hot air balloon going upward at an acceleration. the force of air pushes it up, the force of the helium gas in the balloon keeps it down, and then obviously the weight of the load is a downward force as well. the sum of all the forces together will correspond with the acceleration of the balloon, and heres the key: *as the weight of the load increases, the acceleration will approach 0*. since we're looking for the max load that can be lifted by the balloon keeping it at accel of 0, our equation becomes: sum of forces = Wload (weight of the load) p(air)*g*V - p(hydrogen)*g*V = W(load) and we know W(load) is just mass(load)*g so final eq: p(air)*g*V - p(hydrogen)*g*V = mass(load)*g the g's cancel out!!! (this helps us elim option B left with option A.

Q6. Which of the following best describes the behavior of air parcels in the atmosphere when the value of the CAPE is negative? a) parcel remains stationary b) parcel moves horizontally c) parcel rises upward d) parcel sinks downward

parcel will sink, its D! so I knew that CAPE being neg means Wb will be neg (obviously).. just looking at the given equation there. but then I was lost. to get this I just had to know that a negative F(buoyancy) legit means that the parcel will sink downwards there's a whole formula that outlines this concept! (newtons 2nd law of motion) Fnet = F(b) -F(g) net force = force of buoyancy - force of gravity (if the weight of the objects is higher than the force of buoyancy the thing will sink, and net force is negative. it must sink bc buoyancy force is always directed upwards)

Q4. Which image best illustrates the vector difference bw the vector 15 and vector 10?

so incredibly silly here I would have gotten this right!! I added the vectors, but QUESTION ASKED FOR SUBTRACTION!

Q27. A radioactive atom decays by 5 alpha, 3 beta minus, and 2 gamma emissions to yield 211Po. What was the original nucleus? a) 231Pa b) 223At c) 231U d) 191Ir

the shocking revelation of this question is that I learned that beta minus (and beta plus for that matter) decay reactions actually change the atomic number (thus the element the atomic # defines)!! I had thought that beta minus decay meant that a negative charge was emitted (like an electron was released) so the charge of the resulting atom is positive - which is true! but when talking about decay, this actually means that the atomic element its referring to changes. in beta minus decay, a negative particle is emitted and so the charge (bottom number/element #) increase by +1. in beta plus decay, a postiive particle is emitted, so the charge (bottom number/element #) decrease (-1).

Q 15. A charged particle is accelerated in a uniform electric field. When its velocity is 2 m/s, its electric potential energy is 100 J and its kinetic energy is 10 J. What is the particle's potential energy when its velocity reaches 4 m/s? a) 25J b) 70J c) 90 J d) 135 J

this isn't a hard problem, I just didn't know a formula and so couldn't solve it I had to know that this was the equation to use here: PEi +KEi = PEf + KEf and solve for PEf we have all the info necessary to get there you identify the KEf by using the KE equation KE = 0.5mv^2 and you can find mass by using the known info for the KEi and solve for m, and use that m in the KEf equation simply maths! just gotta remember these formulas

P37. When the side of an open tank filled with water is punctured, water flows out according to Bernoulli's equation: P1+12ρv12+ρgy1=P2+12ρv22+ρgy2 where P is the external pressure, ρ is the density of water (103 kg/m3), v is the flow velocity, g is gravitational acceleration (10 m/s2), and y is the elevation. If water flows out at a rate of 6 m/s, what is the height of the water above the hole? a) 1.0m b) 1.3m c) 1.6m d) 1.8m

this question was allll about Bernoulli. this triggered my fight or flight too lol bc so many terms! but remember... in this shit, so many terms get cancelled - esp in "water flows from a hole in a tank type problems" so basically starting with the whole equation: P1 or P2 is just referring to the external (atmospheric pressure). this doesn't change so these terms can cancel. then left with the pgh term (potential energy) initial + 0.5 pv^2 (kinetic energy) initial = pgh (final) + 0.5mv2 (final) the initial's v^2 term is actually so negligible that it can be thought of as 0. (Think about it: the velocity at which the water level falls in the tank is so little compared to the velocity of water flowing out of the hole... so its not significant enough and can be excluded). another thing that can be excluded is the pgh(final) term because we take set the baseline of "zero" to be at the point of the hole. and we're trying to identify what "h" is which is how much distance from the hole to the surface of the container. SO: Shortcut to use for this exact type "water flowing from hole in a tank" situation: pgy(1) = 0.5pv(2)^2 density terms can cancel on both sides: gy(1) = 0.5v(2)^2 Solve for y (height/ or distance from hole to top) and you're done! answer is: d. 1.8m

Q12. Which of the labeled interactions in Figure 1 are dipole-dipole interactions between permanent dipoles? I, II, III, IV are the options answer: I and II only.

this was a little tricky in that I had to recognize the difference bw dipole-dipole, versus other similar things like dipole-induced dipole, ion-dipole etc. the first two are interactions bw things that already have a partial charge (so they are official dipole dipole and this is the answer) the third one is a H2O molec trying to interact with an H substituent and thereby inducing a dipole in that H. so this is NOT dipole dipole, its induced dipole. last one is ion-dipole; that oxygen has a straight up negative charge and is an ion.

Q45. Laser Doppler vibrometers detect the Doppler shift of a laser beam reflected off an individual's chest to measure respiratory rate. The calculated displacement of the chest during a breath using a 500-nm laser is shown below. (graph) - showing a displacement/velocity curve, with two points having a slope of 0, and 1 point with a negative slope If the laser source is stationary, at which point(s) would the observed frequency of the reflected laser be 6 × 1014 Hz? a) II only b) I and II only c) I and III only d) II and III only

this was a tough one... I also didn't know some things that I needed to , to get this. so I guessed randomly here I needed to know: velocity = wavelength*frequency and then also needed to know the concept of Doppler shift, which tells us that when there is relative motion bw a wave source and an observer, the observed wave frequency and wavelength is diff than what it actually originally is. in this q, the "original" or given light beam's wavelength is given 500nm, and we know its velocity bc its light, so c = 3*10^8 m/s with these 2 things, we are able to calculate the "original" frequency using velocity = wvlenght*frequency equation freq is calculated to be: 6*10^14. Lo and behold this is the same as the observed frequency!! what!? so that *must* mean that the laser beam source isn't moving at all.. the freq is exactly the same. now, where on a displacement-time graph can you find when something is not moving at all? when its velocity is 0. meaning on this graph, its slope is 0. That's at points I and III, so option C is your answer.