I'm sure most people here have heard about the microwave "invisibility cloak" that was made with metamaterials. For those that haven't heard, basically electrodynamics can be rewritten to handle changes in refractive index of materials with GR like tools where instead the background is...
Applying Newton's 2nd law?!
Homework Statement
A 2.91 kg block starts from rest at the top of a 32◦ incline and slides 1.98 m down the incline in 1.28 s.
The acceleration of gravity is 9.8 m/s2
What is the acceleration of the block?
Answer in units of m/s2
What is the coefficient...
Homework Statement
A man standing in an elevator that is moving with a constant acceleration holds a 3-kg block B between two other blocks in such a way that the motion of B relative to A and C is impending. Knowing that the coefficients of friction between all surfaces are μs = 0.30 and μk =...
Homework Statement
There is a box on a platform with mass 3.5kg and it has two ropes connected to it. On the end of each of these ropes are 2 other boxes hanging off the table (so only F_y component). One box is 2.5kg and the other is 1.5kg. I need to find the acceleration of all the boxes...
Suppose A box represents the universe. It also has a battery and a propellor inside it. The propellor is supposed to increase the temperature of the whole universe including itself and the battery.
If this hypothetical universe is initially at 25 degrees C, then we incresed this temp to 27...
Does a black hole radiate infrared waves? If not, then it could absorb some of the infrared waves from a colder object, perhaps one orbiting the black hole, in apparent violation of the 2nd law of thermaldynamics.
Homework Statement
A chain consisting of five links, each of mass 0.090 kg, is lifted vertically with a constant acceleration of a = 3.6 m/s2. Find the magnitude of the force that link 3 exerts on link 2.
Note: The chains are connected vertically
Homework Equations
\Sigma F = ma The Attempt...
Brand new to the forum. My apologies if this problem is already posted on the site. I searched a bit but had no luck.
Homework Statement
Problem from Cutnell & Johnson PHYSICS 7th Edition. Chapter 4 - Problem #9
Two forces FA and FB are applied to an object whose mass is 8.0 kg. The...
Homework Statement
10-42 shows particles 1 and 2, each of mass m, attached to the ends of a rigid massless rod of length L1 + L2, with L1 = 0.80 m and L2 = 6.2 m. The rod is held horizontally on the fulcrum and then released. What are the magnitudes of the initial accelerations of (a)...
http://en.wikipedia.org/wiki/Maxwell%27s_demon"
when i read this i was wondering, what if the deamon accuires no information at all and just shoots blind by guessing wherever a approaching particle is A or B..
in most cases the demon would end up with a no separation, but if its lucky...
Homework Statement
Is it possible to find the P.D. across the 10ohm resistor.
Homework Equations
Kirchoff's second law.
The Attempt at a Solution
Well KSL states that the sum of the pds is equal to the sum of the emfs.
I(10) + 0.25(12) = 2
Gives the wrong value for...
ok, the lorentz force equation is F=q(E+v x B) and Newton's 2nd law is F=ma. I need to combine the two to show that ma.v=qE.V
I don't really know what to do first here...
i can see the simple substitution so that ma=qE+q(v x B) but beyond that...do u change the a to dv/dt. Any type of help...
Is my proof of Kepler's 2nd law correct?
area of sector of circle/ellipse (that the planet sweeps out): (1/2)(r^2)O
O is theta!
dA/dO = (1/2) (r^2)
dA= (1/2) (r^2) dO
dA/dt = (1/2) (r^2) dO/dt
It can't be that simple? Can it??
I would apreciate some proof-readers giving their comments on my answer to an assignment for Undergrad Physics 2nd Year.
Homework Statement
Question: Give an explanation of the 2nd law to an intelegent non-scientific lay-person, drawing ideas from the K-P Statement, C's Statement and the...
Thermodynamics 2nd Law Please Help! :(
I am going crazy trying to understand the Kelvin-Plank statement for the 2nd Law of Thermodynamics. It states:
"It is impossible for any system to operate in a thermodynamic cycle and transfer energy by work to the surrounding while receiving heat from a...
The classical version of that law includes a definition of a system and entropy increasing over time.
It uses a notion of simultaneousity - we compare a state of the whole system in different moments of time.
My questions:
1. Do you know any good SR-compatible generalizations of that...
Homework Statement
A sled moves on the flat surface of a hill. The hill makes an angle θ with the horizontal, and is left orientated.
The hill: θ = 60°; left oriented; μk = 0.1.
The sled: mass = 20 kg; starting location = 20 m from the bottom of the hill;
initial speed = 0 m/s ...
Homework Statement
An electric generating station is designed to have an electric output power 1.20 MW using a turbine with two-thirds the efficiency of a Carnot engine. The exhaust energy is transferred by heat into a cooling tower at 98°C.
(a) Find the rate at which the station exhausts...
Homework Statement
Heat is transferred into saturated liquid water until it is saturated vapor. The water remains at 300 C throughout the process.
a. What is the initial pressure?
b. What is the final pressure?
c. How much heat is transferred per kg of water?
I'm having trouble...
I stand on the outermost planet orbiting the outermost star of the outermost galaxy of our universe. I turn on my flash-light and I can be sure that the beam of light will not hit any object. After I turn it on, I cannot recover the photons or prove they ever existed, so does it mean I decreased...
Taking S=kln\Omega to define entropy, it follows immediately that \frac{dS}{dt} \geq 0 holds as a statisical law so long as we assume equal a priori probabilities for each microstate. It seems that so long as we use the Bayesian interpretation of probability, the second law does not need to...
Homework Statement
A person pushes a 16.0 kg lawn mower at constant speed with a force of 75.0 N directed along the handle, which is at an angle of θ = 40.0° to the horizontal.
Calculate the normal force exerted vertically upward on the mower by the ground.
Calculate the force the person must...
Homework Statement
A tennis player strikes a tennis ball of mass 56.7 g when it is at the top of the toss, accelerating it to 68.0 m/s in a distance of 0.0250 m. What is the average force the player exerts on the ball? Ignore any other forces acting on the ball.
Homework Equations
f = ma...
Hi,
I feel extremely stupid for having to have this explained to me, but I am really confused by it. I recently encounter a proof of the fact that the brightness (energy/(time x area x solid angle x frequency)) of a black body can only depend on its temperature, not the properties of the...
Homework Statement
How does life violate the 2nd law of thermodynamics?
Homework Equations
The 2nd law states that with ever energy transformation entropy increases.
The Attempt at a Solution
I am not sure where to begin with this. All I can think of is as we evolve our system...
A helicopter is moving horizontally to the right at a constant velocity. The weight of the helicopter is W = 57600 N. The lift force L generated by the rotating blade makes an angle of 21.0° with respect to the vertical.
(a) What is the magnitude of the lift force in N?
(b) Determine the...
Homework Statement
The problem reads: "If the Earth were suddenly to stop in its orbit, how long would it take for it to collide with the Sun?[Regard the Sun as a fixed point mass. You make use of the formula for the period of the Earth's orbit.]" (The answer is 65 days. Obviously, I'm not...
I have a question:
Al and Bert stand in the middle of a large frozen lake (frictionless surface). Al pushes on Bert with a force of 20 N for 1.2 s. Bert's mass is 114 kg. Assume that both are at rest before Al pushes Bert.
(a) What is the speed that Bert reaches as he is pushed away from Al...
Homework Statement
The 10-Mg truck hauls the 20-Mg trailer. If the unit starts from rest on a level road with a tractive force f of 20 kN between the driving wheels of the truck and the road, compute the tension T in the horizontal drawbar and the acceleration a of the rig.
Homework...
So i have a few questions in relation to a practical completed in grade 11 Physics
The basic experiment about the 2nd law, in which a hanging weight is used to accelerate a cart
the practical also had a 2nd part in which weights were added to the small cart to decrease the acceleration while...
Homework Statement
http://ready2goxtr.googlepages.com/problem1055.jpg
A cylinder having a mass of 2.0kg can rotate about its central axis through point O. Forces are applied as show: F1 = 6.0N, F2 = 4.0N, F3 = 2.0 N, and F4 = 5.0N. Also, r = 5.0cm and R = 12 cm. Find the (a) magnitude and...
Homework Statement
A man walking with aid of a cane approaches a skateboard (mass 3.5 kg) lying on the sidewalkk. Pushing with an angle of 60 down from the horizontal with his cane, he applies a force of 115N, which is enough to roll the skateboard out of the way.
a) calculate the...
Homework Statement
http://ready2goxtr.googlepages.com/problem1052.jpg
A uniform disk that can rotate around its center like a merry-go-round. The disk has a radius of 2.00 cm and a mass of 20.0 grams and is initially at rest. Starting at time t = 0 two forces are to be applied tangentially...
http://www.newscientist.com/channel/fundamentals/mg19826614.400-physicists-atomsorting-demon-created-with-lasers.html?feedId=online-news_rss20"
"The demon appears to bring order to chaos without expending energy, violating the second law of thermodynamics. "
So correct me if I am...
1. A 4.0kg object is attached to a vertical rod by 2 strings. Object roatates in a horizontal circle at a constand speed 6.00 m/s. Find the tention in the upper and lower string. The strings are 2 meters long. the distance between the attachment points for each string is 3 meters.
2...
Chemical reaction have 2 classifications: Exothermic and Endothermic.
Exothermic is when the chemical give off heat in the reaction.
Endothermic is when the chemical obsorb heat in the reaction.
So... If one exploit Endothermic reaction by keep taking heat from the low temperature heat...
Time, or rather the arrow of time, is defined within the 2nd law of thermodynamics: The future is in a higher entropy state than the present, which in turn is in a higher entopy state than the past.
But when the universe, our isolated system, reaches the maximum entropy state - heat death -...
Homework Statement
Ok this is kind of long. This is the 4th question on my homework assignment and I need to give background on the first 3 to make sure I got those correct.
1. I am sure on this since it was simply finding the weight of a rocket ship that has an intial mass of 3kg. Answer is...
I was reading a physics textbook. It is stated that force is defined by mass and acceleration (a force of 1N causes a mass of 1kg to accelerate at 1ms^-2). In later part, it is stated that mass is defined by force and acceleration (a mass acted by a force of 1N accelerates at 1ms^-2 is 1kg). As...
Homework Statement
A particle moves under the influence of a central potential V(r). Show that Kepler's second law, that the radius vector from the force centre to the particle sweeps out area at a constant rate, is true whatever the form of V, as long as it is central. Derive the law in the...
Homework Statement
A 1 kg object is moving along at speed of 5 m/s right before colliding with a 4 kg stationary object, in a perfectly inelastic collision.
Suppose that the objects are moving on a surface that has a coefficient of friction of mu=0.2. (Note you may still assume that the...
Homework Statement
Daytona International Speedway in Florida. Both of its courses feature four story, 31.0 degree banked curves with max radius of 316 if a car negotiates the curve too slowly it tends to slip down the incline of the turn whearas if it going too fast it may begin to slide up...
Homework Statement
The driver of a car whose mass is 1200kg is traveling 45km/h[W] on a slippery road when he applies the breaks. The car skids to a stop in 35m. Determine:
a) the car's acceleration
b) the net force acting on the car
c) the coefficient of friction between the tires and the...
Homework Statement
(a) If R = 12 cm, M = 500 g, and m = 50 g (below), find the speed of the block after it has descended 50 cm starting from rest. Solve the problem using energy conservation principles.
- The pulley is setup on the corner of a desk with the object hanging from it. M is the...
Homework Statement
An arrow, starting from rest, leaves the bow with a speed of 25.0m/s. If the average force exerted on the arrow by the bow were doubled, all else remaining the same, with what speed would the arrow leave the bow?
Homework Equations
F = ma
The Attempt at a...
I read from Victor Stenger's books that maximum entropy exists in black holes or singularities. So, at the Big bang, the universe had its maximum entropy. Does it mean that entropy has DECREASED since then? Stenger explained that since the universe expands, it has more space for entropy...
Homework Statement
A solid cylindrical disk has a radius of 0.16 m. It is mounted to an axle that is perpendicular to the circular end of the disk at its center. When a 45 N force is applied tangentially to the disk, perpendicular to the radius, the disk acquires an angular acceleration of 110...
Hi, I'm having trouble with a problem dealing with Newton's Second Law, and was wondering if anyone could give me a hint as to how I should solve it (general equation, process, whatever)? I'm not asking for somebody to solve it, I just need some help...:smile:
Homework Statement
A...