1. ### Torque on a circular current loop

Can anyone please tell me why the torque on a circular current loop can be calculated by the equation below? In other words, what is the intuition for the formula? Thank you. (I modified my question to a particular case) $$\vec{\tau} = I \vec{A} \times \vec{B}$$
2. ### Why Can We Consider a Conducting Sphere as a Point Charge When Finding Its Electric Field?

This page claims that "[t]he electric field outside the sphere is given by: ##{E} = {{kQ} \over {r^2}}##, just like a point charge". I would like to know the reason we should treat the sphere as a point charge, even if the charges are uniformly distributed throughout the surface of the...
3. ### Courses AP Bio then AP Physics 1 or other way around?

Hey! I’m a sophomore that is scheduling for next year. Hopefully, I will be taking AP Calc BC next year (junior year). As for my science course, I want to take AP Bio and AP Physics 1 before graduating, but we can only take one per year. So would you recommend Physics during my senior year when...

Homework Statement Your consulting agency, with its extensive knowledge of physics, has been subpoenaed to provide expert testimony at an automobile accident case in civil court. The case involves a crash between a Ford Escort car and a tractor-trailer truck. 1. The police department...
5. ### When is Work done by Force Negative or Positive?

Is it confusing to find when is Work done by a force negative or positive? It indeed can be. Learn in this chapter how the dot product of force and displacement can give you the value of work done by the force and also if it is negative or positive
6. ### Simple Harmonic Motion/Fundamental Frequency

Homework Statement A tuba is a instrument that can be modeled after a closed tube and has a length of 4.9m. A frequency of 122.5hz produces resonance in the Tuba. Is this the fundamental frequency of the instrument? If not, what harmonic is it? Homework Equations f=λv 4l=λ(open closed tube) v=...
7. ### Force problem with three masses and two pulleys

Homework Statement For the apparatus in the figure, what is the minimum value of the coefficient of static friction between the block (m3) and the table that would keep the system at rest if m1 = 0.10 kg, m2 = 0.20 kg, and m3 = 0.30 kg? (Assume ideal conditions for the string and pulleys.)...
8. ### Courses Homeschooling AP Physics C?

I have decided to go home schooled for my last two years of high school and I am trying to make a curriculum at the moment. Do any of you know a good resource for this? It has not been too hard to find a physics 1 or 2 course, but calculus based physics courses have been pretty sparse. So far I...
9. ### Finding internal resistance & EMF of a battery in a circuit

Homework Statement When an external resistor of resistance R 1 = 14 Ω is connected to the terminals of a battery, a current of 6.0 A flows through the resistor. When an external resistor of resistance R2 = 64.4 Ω is connected instead, the current is 2.0 A. Calculate the emf and the internal...
10. ### Masses connected to spring momentum

Homework Statement An m = 1.3 kg block and an M = 3.0 kg block have a spring compressed between them and rest on a frictionless table. With a stopper in place that prevents m from moving, the spring is compressed and released so that M moves away with a speed 2.0 m/s. The spring is...
11. ### Block sliding on top of cart

Homework Statement A block of mass m =0.75 kg is set on a large cart of mass M = 6.5 kg. The cart's rollers are frictionless, but there is a coefficient of kinetic friction of 0.36 between the cart's surface and the block. The cart is at rest when the block is given an initial speed of 5.2...
12. ### Postion vs time graph without time or initial speed?

Homework Statement Consider the system shown to the right. Particles 1 and 2 are fixed in place while particle three is placed at the location shown and released. Let’s look at the mechanics of q3, which has a mass of 3.00 X 10-5 kg. What will be the net force on q3? What will be...
13. ### Work and energy

Homework Statement This is for my ap physics summer work and is giving me some trouble and could use any help A small block, with a mass of 250 g, starts from restart the top of the apparatus shown above. It then slides without friction down the incline, around the loop then onto the final...
14. ### When do I use Biot-Savart Law vs. Ampere's Law?

This isn't a homework problem, I have the solutions for this problem. I'm just wondering why, for question 3, letter a, part ii, it's necessary to use the Biot-Savart law instead of Ampere's law? What are the use cases for Biot-Savart law vs. Ampere's law...
15. ### Physics in everyday life

Hi there! So to wrap up the year in AP Physics 1, we have to take videos or pictures of physics in everyday life. Two of my situations are: 1. Situation where you have greatest net torque 2. Situation where acceleration changes both speed and direction at same time For the first one, I was...
16. ### Spinning Ice Skater Question

So basically, I was doing my AP Physics 1 homework and came across the spinning ice skater question yet again. The question states, "An ice skater is spinning about a vertical axis with arms fully extended. If the arms are pulled in closer to the body, in which of the following ways are the...
17. ### Collision Investigation (2-D)

Homework Statement I apologize in advance because this is a long question. This is a scenario based question where I role play as an intern for the Montreal Police Collision Investigation Unit. Basically I have to determine the initial velocity of vehicles to determine whether or not they are...
18. ### Testing AP Physics 1 and 2

Hi, When I am using Principles of Physics by Walker, Halliday, and Resnick to study for AP physics 1 and 2 exams, what chapters/subject areas should I focus on to get at least grade 3? Due to a lack of time to study I will need to study what's most important. Alternatively, recommendations for...
19. ### Finding Centripetal acceleration in a vertical system

Homework Statement Tarzan plans to cross a gorge by swinging in an arc from a hanging vine. If his arms are capable of exerting 1350 N on the vine, what is his acceleration at the point where the vine makes an angle of 45 degrees from the vertical assuming maximum speed at this point. His mass...
20. ### Find the final velocity of the block

Homework Statement So here is the problem, There is a .03kg block that is in an inverted cone, the cone has a slant length of 15 cm and a radius of 4 cm, and the coefficient of friction is .35. The block rotates around the inside of the cone, seamlessly, until it hits the bottom of the cone...
21. ### Help explain Physics Phenomenon

http://www.quora.com/How-can-sound-waves-alter-the-flow-of-water [Broken] Ok, so I carried out this experiment, and I understand some of it, but need help with other parts. Ok, so are we actually seeing a sine wave formed by the water? If so, I understand that waves are supposed to transport...
22. ### Other AP textbooks for Physics and Calculus

Hi, I'm studying on my own for AP exams a year from now and need some advice on which books to get. I'm taking AP calculus (AB or BC, haven't decided yet), AP Physics 1, AP Physics 2, AP Physics C: Electricity and Magnetism, and AP Physics C: Mechanics. I already have a Calculus book by Ron...
23. ### Uniform Circular Motion question

1. The problem The answer is A. Homework Equations x = Acoswt y = Asinwt The Attempt at a Solution C is not correct because the x & y positions are in terms of sin & cos, so the acceleration can't be constant. D is not correct because x & y are oscillating in value. E is not correct because...
24. ### Escape velocity problem

1. Problem A rocket has landed on Planet X, which has half the radius of Earth. An astronaut onboard the rocket weighs twice as much on Planet X as on Earth. If the escape velocity for the rocket taking off from Earth is v , then its escape velocity on Planet X is a) 2 v b) (√2)v c) v d) v/2 e)...
25. ### Finding propagation speed/wavelength from an equation

Homework Statement A wave is described by y=12sin(4t-8x). What is its propagation speed? A. 0.2 B. 0.5 C. 4 D. 8 E. 12 Homework Equations v=wavelength/period v=wavelength×frequency The Attempt at a Solution period= 2π/w=2π/8=.7853 But confused on how to find the wavelength?
26. ### Conservation of Angular Momentum & Energy question

Question: A streetcar is freely coasting (no friction) around a large circular track. It is then switched to a small circular track. When coasting on the smaller circle its speed is: a) greater b) less c) unchanged Relevant Formulas: w = v/r KE = 1/2mv2 My teacher said the normal force from...
27. ### AP Physics ~ A good jump in the long jump event is

A good jump in the long jump event is 3.7m. If the jumper leaves the ground at an angle of 25°, what speed must he need to jump the 3.70m distance? →Could you use this equation: vf²=vi²+2aY aka (final velocity)²= (initial velocity)²+2(acceleration)(distance in the y-direction) →So, that...
28. ### Projectile Motion ~ AP Physics (A rifle is fired at an angle of )

A rifle is fired at an angle of 25° below the horizontal with an initial velocity of 400 m/s from the top of a cliff 60.0m high. How far from the base of the cliff does the bullet land? This is what I did, but i'm not sure if its right: y-component→ v=400sin(25°) ∴v=169.05 x-component→...
29. ### AP Physics C lab involving incline planes featuring motion laws

Homework Statement A dot on the floor with a diameter of 2cm. A table that is at a distance of 46cm horizontally from the center of said dot. The table is 90cm tall. The meat of the problem: A ping pong ball rolls off an incline plane (a wooden board) that is on top of the table. The...
30. ### AP Physics B Course Description Multiple Choice #3-4

Homework Statement http://apcentral.collegeboard.com/apc/public/repository/ap-physics-course-description.pdf Page 45 Homework Equations sinθ = opp/hyp tanθ = opp/adj cosθ = adj/hyp G ≈ 10 m/{s}^2 The Attempt at a Solution I know that the weight is a force pointing downwards...