# Introductory physics Definition and 51 Discussions

The following outline is provided as an overview of and topical guide to physics:
Physics – natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.

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1. ### Force between 2 point charges in VECTOR format (x i + y j + z k)

I tried using the distance between r2 and r1 and plugging them into the equation for i, j, k. >> So for the force in the x direction it was k*(4E-6*4E-6)/(4-9)^2. The answer I got was wrong according to webassign. Can someone please tell me what I am missing?
2. ### Problem involving Torque and a Derrick from Feynman Exercises

I attempted to solve this problem by considering the torque caused by the perpendicular components of the tension and weight with respect to the derrick. $$Tcos\theta x = Wsin\theta L$$ $$T = \frac L x Wtan\theta$$ Using the principle of virtual work I also arrived at the same answer by...
3. ### Calculate the best angle for maximum light dispersion through a medium

I first thought that the angle would have to be maximum when it is closest to the critical angle for total internal reflection. From my lectures the equation for the critical angle is ##\theta _1>\ sin ^{-1} \left( \frac {n_2} {n_1} \right),## so as ##n_2 = 1##, we have ##\theta _1=\sin...
4. ### Entropy Change & Heat Transferred to a Gas

By using the given relationship that S=a/T --(1) along with the equation ∫ (delta Q rev)/T=∫dS -- (2) I found out that my answer for the value of Q is mc*ln (T2/T1)*a upon equating (1) & (2). But the solution is instead given as Q=a*ln*(T1/T2). I would be grateful if someone would point out...
5. ### Question on RMS Mean Free Path

lambda (rms)= v(rms) * t(rms) -- 1 Now I assume here that t(rms)=1/(√2*n*π*d^2*v(rms)) But this cancels the v(rms) term when used in eq (1) so the mean free path and the RMS free path would actually be the same (even later on when used in the aforementioned Survival Equation) I would like to...
6. ### To find total work done from multiple reversible processes

The question is given in 3 parts. For first part, process is isochoric so Work done=0. We know here that at end of the process (a), T2=T1 while V remains constant (we can take it as V1) so P2=2P1. For second part, process is isothermal so T is constant. At end of process we reach P1 again from...
7. ### Work & Energy (Question on Classical Mechanics/Slope based Problems)

I used the Change in Kinetic Energy and equated that with the Work Done. The "Work Done" part comprises of two different functions- one is work done by Gravitational Force while the other is the work done by frictional force (or the brakes). /Delta KE (magnitude wise)= 0.5*1350* (20^2)=270,000...
8. ### Maxwell's Distribution Law (Thermal Physics)

There are two questions in the photo. I have attempted the solution (attached below) and I would be highly obliged if someone would verify the same. Edit- Sorry the images of the solution have uploaded in the wrong order. 5th and 1st Image comprise of both parts of Q1 while the remaining of Q2.
9. ### Question on First Law of Thermodynamics (Paramagnet)

For the first part, I have expressed it in the following differential form- dU= delta (Q) + BdM Now for the second part I am having major confusion. I know that B corresponds to P and M corresponds to V as generalised force and generalised displacement respectively for a Paramagnetic substance...
10. ### I Fluids: Bernoulli's Equation Derivation Question

I figure that either the Force F2 is applied in the opposite direction because of some kind of resistance, but I'm not sure. Thanks!
11. ### A Graph analysis problem to find when the acceleration is zero

I had deduced that B,E,H are the places where acceleration will be zero, but when I read the solutions it showed that K also has a = 0. It said it had maximum slope and then said a = 0. But I couldn't understand why? Please help.
12. ### Using Impulse to Solve For the Final Velocity

Hi there, Just asking a logistics question since I want to be sure I am approaching this problem correctly. My professor showed me an example of a bullet being fired from a barrel, given its initial velocity was 0. The change in time was 0.1 seconds. The mass of the bullet is 0.02 kg. The...
13. ### Magnetic field on a loop due to another loop

In the attached picture, the outer wire is carrying a current I(t), and it's asked to find the induced EMF in the inner loop. Now I have indeed calculated the B-field along the z-axis due to the outer loop. My lecturer then puts z=0 into that expression and then multiplied it with the area of...
14. ### Universal Gas Equation problem

Hi everyone, I'd really appreciate any help with this problem: A helium cylinder for the inflation of party balloons hold s 25.0L of gas and is filled to a pressure of 16500kPa at 15 degrees celsius. How many balloons can be inflated from a single cylinder at 30 degrees celsius if the volume of...
15. ### Studying What books are good to learn the math in intro physics?

I'm struggling with the math used in my college's calc-based honors physics class, even though I've taken calculus 1. ---What are some good books/resources to learn the math used in introductory physics?--- Preferably, it'd be nice if the math was taught using examples in physics. Having that...
16. ### Courses Is it okay to not understand the calculus in intro physics?

I don't understand a good portion of the non-algebraic math behind much of the physics in my first semester college class. I understand everything with algebra, and can solve all problems, but I don't understand the relationships with vector cross/dot products, calculus derivations, DE, etc...
17. ### What angle will give the object the greatest range?

Homework Statement 1-A rifle can shoot a projectile with a velocity of 207m/s. At what angle should the rifle be pointed to give the maximum range? 2-Evaluate the maximum range Homework Equations N/A The Attempt at a Solution I considered at first that the problem seemed like it could be...
18. ### Struggling with a free-fall question

Homework Statement Two stones are thrown simultaneously, one straight upward from the base of a cliff and the other straight downward from the top of the cliff. The height of the cliff is 6.00m. The stones are thrown with the same speed of 9.0m/s. Find the location (above the base of the cliff)...
19. ### Database of physics powerpoint slides?

Is there any website that has a database of physics (or other course) powerpoint slide sets? For example, I am teaching both an introductory physics class, and a separate calc-based physics class of what should be the same general material as the non-calc-based. For the former class I am using...
20. ### An equilateral triangle's electric field at its center

Homework Statement Three 18-cm long rods form an equilateral triangle. Two of the rods are charged to +10 nC, and the third to - 10 nC. What is the electric field strength at the center of the triangle? Homework Equations $$\vec{E} = \frac{k*q}{r^2}$$ The Attempt at a Solution 1. Draw...
21. ### Angular momentum and rotational energy

Homework Statement A school playground has a carousel, which is simply a circular platform that can rotate around its center axis with negligible friction. This carousel has radius r=1.6 m and rotational inertia I= 177m^2kg. Suppose you are standing beside the carousel which is already spinning...
22. ### Refraction Problem

1. The problem statement, all variables, and given/known data A scuba diver is underwater. She looks up and sees a bird flying in the sky. Compared to its actual distance, the bird appears to be... 1. Closer 2. At actual distance 3. Further Homework Equations n1sin(θ1)=n2sin(θ2) The Attempt at...
23. ### General Definition of Potential Energy - Conceptual Help

My textbook states that an alternative definition of the change in potential energy is the work required of an external force to move an object without acceleration between two points. I am confused on why it says acceleration. Wouldn't that mean that the acceleration is 0 and therefore the...
24. ### Engine Efficiency

Homework Statement An ideal gas with Cv = 5 2R, and γ = 1.4 starts at a volume of 1.5m3 , a pressure of 2.0×105Pa ,and a temperature of 300K. It undergoes an isobaric expansion until the volume is V , then undergoes an adiabatic expansion until the volume is 6.0m3 , and finally undergoes an...
25. ### Ideal Gas Law -- Isobaric Epansion followed by....

Homework Statement An ideal gas with Cv = 5/2R, and γ = 1.4 starts at a volume of 1.5m3 , a pressure of 2.0×105Pa, and a temperature of 300K. It undergoes an isobaric expansion until the volume is V , then undergoes an adiabatic expansion until the volume is 6.0m3 , and finally undergoes an...
26. ### Carnot Cycle

A refrigerator operates on a Carnot cycle. In this cycles, it absorbs 120 J of energy at a temperature Tc while 300 J of work is done on the gas undergoing the cycle. How much energy is exhausted as heat during this process? The answer is 420 J. I am unsure of where to start for this...
27. ### How to solve this pendulum problem?

Homework Statement For number 3,4,5 https://s4.postimg.org/qbp3xzq65/IMG_1092.png https://s22.postimg.org/u220j60sx/IMG_1093.png Homework Equations Centripetal force = m v^2/R T = centripetal force + w Sigma F = m.a The Attempt at a Solution Number 3. Find the v at D point using...
28. ### Torque on a Cylinder

Homework Statement A cylinder having a mass of 5.0 kg can rotate about its central axis through point O. Forces are applied as shown in the figure: F1 = 5.0 N, F2 = 6.0 N, F3 = 2.5 N, and F4 = 5.5 N. Also, R1 = 6.5 cm and R2 = 12.0 cm. Find the magnitude and direction of the angular...
29. ### A falling stone takes 0.28 s to travel past a window 2.2 m...

Homework Statement A falling stone takes 0.28 s to travel past a window 2.2 m tall. From what height above the top of the window did the stone fall? So from this problem I think I have these variables: vo = ? (or 0 because falling usually indicates 0 for an initial velocity?) yo = 0 y = 2.2m...
30. ### How would you find Va and Vb in the problem below?

Hi I am new the site and have to complete this physics summer work from a not so clear textbook. I am also new to a lot of the concepts and material. I was unsure on how i go about solving velocity a and b in this problem: any help is appreciated
31. ### Dimensional Analysis Pendulum Equation

Homework Statement The period of a simple pendulum, defined as the time necessary for one complete oscillation, is measured in time units and is given by T = 2π ℓ/g where ℓ is the length of the pendulum and g is the acceleration due to gravity, in units of length divided by time squared. Show...
32. ### Intro Physics Which book to read the summer before starting Physics?

I'm starting my 1st year of Physics at university in September. Although I've learned a lot of single variable Calculus and various topics of Physics this year, I'd like to get a general overview of the topics touched in a 1st Physics course at uni. I just wonder if there's an equivalent to...
33. ### Curves on a Position time graph

Homework Statement Homework Equations The Attempt at a Solution I knew the answer was between A and B, but the inward curves and outward curves on the position time graph confused me , what exactly does it mean? -does A have an increasing velocity and then B has a decreasing velocity? I am...
34. ### How to calculate average velocity given distance and time?

Homework Statement A motorist drives north for 35.9min at 73.3km/hr and then stops for 15.4min. He then continues north, traveling 114.5km in 1.93hr. What is his average velocity? Homework Equations avg velocity = xf - xi / time The Attempt at a Solution 35.9 min * (1 hr / 60 min) = 0.5983...
35. ### Find the tension in the rope pulling a box at an angle

Homework Statement Homework Equations The Attempt at a Solution Here is what i have done so far: Fx = cos 45 T - Ff =ma Fy=sin 45 T -mg+ Fn =ma I found ff= uk * Fn = 0.5 *sin 45 +mg fn = sin 45 +mg Isolated for T in the x and y: Tx = ma + Ff / cos 45 = 13.404 Ty = ma +mg - Fn / sin 45...
36. ### Conservation of Momentum Spaceship Question

Homework Statement The mass of a spaceship is 10012 kg. The spaceship is at rest. Then one part of the ship with a mass of 1000 kg is ejected and emerges with a speed of 112 m/s. What is the speed of the other part? Homework Equations The Attempt at a Solution I tried: pi=pf mivi=mfv2...
37. ### What causes the acceleration?

Homework Statement A table with smooth horizontal surface is placed in a cabin which moves in a circle of a large radius R (figure attached). A smooth pulley of small radius is fastened to the table. Two masses m and 2m placed on the table are connected through a string going over the pulley...
38. ### Finding the deBroglie wavelength: conceptual issue

Hello all! I am new to this forum, though I have been lurking for a long time. I intend to fill out my profile and introduce myself, but finals leave me with little time to spare at the moment. I have this final next week and would like to sort this out beforehand, hence the hasty post! Thank...
39. ### Coulomb's law question

Homework Statement We know that coulomb's law describes the force between two charged bodies as proportional to the magnitudes of the charges and inversely proportional to the square of the distance. Of course, like charges repel and unlike attract. Now theoretically, if we placed two...
40. ### How can I succeed in Physics this time? Will it get better?

So last semester, I withdrew from Physics with algebra and trigonometry. I am currently enrolled with another professor and I hope I excel this time in the course. He seems more attentive and friendly, along with having a noticeable passion for Physics. Today was the first day of class and...
41. ### Calculus Book idea: mathematical techniques in introductory physics

I have a set of class notes that I've been thinking about publishing as a book, and I wonder what y'all thought about it. The book is intended for people who have taken introductory physics, and it is organized by mathematical topic or technique, with a specific focus on calculus. There are...
42. ### Convex Lens and Magnification

Homework Statement You wish to obtain a magnification of -2 from a convex lens of focal length f. The only possible solution is to: A) place a virtual object at a distance 2f/3 from the lens. B) place a virtual object at a distance 5f/3 from the lens. C) place a real object at a distance...
43. ### Phase Difference between Voltage and Current

Homework Statement The circuit above has a 29 resistor and a 11.1 mH inductor. Calculate the theoretical phase difference between the current CPA and voltage VPB if the circuit is driven by a sinusoidal voltage source with a peak amplitude of 3.5 V at the following frequencies: 20 Hz 420 Hz...
44. ### Simple collision between rocks in outer space. Webassign

Homework Statement [/B] Two rocks collide in outer space. Before the collision, one rock had mass 14 kg and velocity ‹4450, −2950, 2250› m/s. The other rock had mass 7 kg and velocity ‹−600, 1900,3600› m/s. A 1 kg chunk of the first rock breaks off and sticks to the second rock. After the...
45. ### Where between two charges does voltage = 0?

Homework Statement If Q1 in the above figure is twice Q2 and both are positive, where can a point of zero potential be found? Homework Equations V = kq/r The Attempt at a Solution I know that eventually I'll have to set it up so that kq/r = kq/r, but my problem is, how do you know where...
46. ### Net Electric Force

Homework Statement [/B] In the above figure, if Q1 and Q2 are positive, where could a negative charge be placed and have a vertically upward net force on it? Homework Equations F = k|q||q| / (r^2) The Attempt at a Solution I wrote the force equations for the negative charge and both positive...
47. ### Calculate the equivalent resistance

Homework Statement Ignore the internal resistance of the battery and assume it is merely a battery. Calculate the equivalent resistance of the circuit. Homework Equations 1/Req = 1/R + 1/R ... (parallel) Req = R + R ... (series) The Attempt at a Solution I know this is fairly simple but I...
48. ### Kirchhoff's Rule Queston

Homework Statement [/B] Consider the circuit above. You are given the following measured values: V = 1.5 V R1 = 100 R2 = 100 R3 = 50 R4 = 50 R5 = 50 Homework Equations Kirchhoff's Loop Rule and Junction Rule The Attempt at a Solution I tried setting this up using the junction and loop...
49. ### Centripetal Acceleration at top of Loop

Homework Statement A roller coaster is on a track that forms a circular loop in the vertical plane. If the car is to just maintain contact at the top of the loop, what is the minimum value for its centripetal acceleration at this point? A) 2g downward B) g downward C) 2g upward D) g upward E)...
50. ### What is the acceleration of the crate?

Problem: A 22.0-kg crate is pulled along a horizontal floor by the ideal arrangement shown in figure below. The force F is 300 N. The coefficient of friction between the crate and the floor is 0.270. What is the acceleration of the crate? Homework Equations F = ma Friction =...