Relative Definition and 1000 Threads

I have a couple questions about relative motion, since I've been reading everywhere that motion is relative... (Feel free to point me to other threads that answer these questions if there are any - I searched and couldn't easily find any) QUESTION #1 So if I'm standing still, and...

Homework Statement What is the easiest way of finding the symmetrical of a point relative to an arbitrary line? (I was asked on an exam to find the symmetrical of a point relative to the line y = x, but that's rather trivial - just switch the coordinates. How can I do it for any arbitrary...

What exactly comprises a relative velocity in special relativity? I find it confusing when distant galaxies can be moving away from the Earth at speeds approaching the speed of light and yet that separation speed contributes nothing to a relative velocity. The usual answer provided is that both...

Edit. I think the topic is misinformative and I don't know how to change it. Hey I have to translate this into english so bear with me. Two spaceships are approaching Earth from two directions along the x-axis. Earth observer(EO) calculates their speeds to be 0,8c each. Calculate at what...

Homework Statement I have a twin brother, and we're 30 years old. If i travel for three years at 2.55 X 10^8m/s (0.85c) while my brother is a rest on Earth, how much older than me will my brother be upon my return?Homework Equations t=To/√1-v^2/c^2 [b]3. Try to work out To=3 T=? V= 2.55 X...

Homework Statement A kayaker needs to paddle north across a 100-m-wide harbor. The tide is going out, creating a tidal current that flows to the east at 2.0 m/s. The kayaker can paddle with a speed of 3.0 m/s. Homework Equations v= v + V Let the Earth frame be S and a frame attached...

Please excuse my ignorance - I am a biologist by training - but this is one of those questions that just keeps bothering me and I can't find the answer with Google/Wikipedia. Take as our example the ocean currents on the Earth caused by the Coriolis Effect of the Earth turning. When I read up...

Hello everyone! I need some help with a Doppler effect/relative motion question. Homework Statement A whistle with a frequency of 1200 Hz is traveling south at a velocity of 30.0 m/s. You are traveling north away from the whistle at a speed if 18.0 m/s. If the speed of sound is 340 m/s, what...

Homework Statement Show that the function f(x) = x\sin\left( \frac{\pi}{x} \right) has an infinite number of relative extrema. Homework Equations The Attempt at a Solution Using the product rule and chain rule to find the derivative f'(x): f'(x) = \sin\left( \frac{\pi}{x} \right) -...

A boat A is chasing boat B along a river by moving in the same direction as the stream. The speed of the river stream is 6 miles per hour, the speed of boat B relative to the river is 48 miles per hour, and boat A is 8 miles per hour slower than boat B. Currently boat B is ahead of boat A...

Homework Statement Let m1, m2 and m3, the mass of 3 particles and v12, v23, v13 their respective relative velocities. a) Show that the total kinetic energy of the system in relation to the center of mass is: ( m1m2v12^2 + m2m3v23^2 + m1m3v13^2 ) / (m1+m2+m3) b) generalize this result...

Hello, Let me first say this is not homework, If you do not believe me you can use any numbers you would like. I am just curious and would like to see how the "speed" of an object changes relative to different things. Basically, if say, I move 10 mph (or 20 mph, or 5 feet a second, it...

Homework Statement Might be the sketch most useful first: The prism is sliding horizontally from left to right under condition : S(t)=4*t*t+5*t+1[cm] and the bar OA is rotating, point A is sliding over the prism's slope and point O is the immobilized center of bar's rotation, OA=10cm...

Greetings, I have a work requirement to calculate building chilled water use based on known supply temp (deg F), return temp (deg F) and flow (GPM). I would like to know the relative error associated with the energy calculation. Based on the product data for the sensing equipment, I know that...

Homework Statement mass of Fuzzy = 100.0kg mass of cart = 200.0kg Homework Equations Conservation of Momentum for 1D Motion Relative Velocity for 1D Motion The Attempt at a Solution Since everything is at rest at the beginning, the total momentum of the system is 0. So at the end, 0 =...

Greetings, I have a work requirement to calculate building chilled water use based on known supply temp (deg F), return temp (deg F) and flow (GPM). I would like to know the relative error associated with the energy calculation. Based on the product data for the sensing equipment, I know...

Homework Statement Two people push in opposite directions on a block that sits atop a frictionless surface (The soles of their shoes are glued to the frictionless surface). If the block, originally at rest at point P, moves to the right without rotating and ends up at rest at point Q...

Hi, I've been listening to a Professor Jim Al-Khalil's scipod on time travel. I think this guy is bloody excellent by the way. http://reader.mac.com/mobile/v1/http%3A%2F%2Fwww.jimal-khalili.com%2Fpodcast%2Fjim.rss Anyway, He said to an observer on the Earth a clock on a...

Hi.. What will be the nature of relativistic mass when a body moves with speed of light..?

When one says they are at rest relative to the cosmic microwave background, does this mean that they are in a frame where the same frequency is measureed in all directions? Because, I could imagine if I boosted in one direction, then the spectrum behind me would be redshifted, and the spectrum...

Homework Statement A boat is crossing the river with a speed of 6.2 m/s east relative to the water. The river is flowing north at a speed of 2 m/s and is 750 m wide. a) What is the speed of the boat relative to the Earth? b) How much time is required to cross the river? c) How far downriver...

Hi everyone Homework Statement Take a look at the drawing. Now I found out the differential equation for this is: \mu \vec{r}''=-k \vec{r} mu is the reduced mass Now I shall show, with using the generel solution for this differential equation (in cartesian coordinates), that the...

Homework Statement Space ships A and B, each having a proper length of 100m, pass each other moving in opposite directions. According to the clocks on ship A, the front end of B takes 1.5 x 10^(-6) s to pass the entire length of A. a) what is the relative velocity of the two ships? b)...

Homework Statement motor is mounted on top of lift. a)if p moves by y, what is the displacement of Pt A? Prove that Vp=-3Va. b)If motor unwidns cable at const rate 2m/s, what is vel of cable wrt lift. Prove vel of lift is 0.5m/s Homework Equations The Attempt at a Solution I...

https://www.physicsforums.com/showthread.php?p=3577768#post3577768" has caused me to question my assumptions. If a target of observation is moving at relativistic velocities but its distance does not change wrt the observer, is it observed to be experiencing time dilation? Alice stands at...

Imagine an Aeroplane held above the Earth's surface for 12 hours, having no contact with the surface of the earth. Suppose that the initial location at time t=0 is Asian continent. So after t = 12 hours, can we expect the aeroplane to be in some other continent or will it be in the same location.

Hi, I am curious whether that when the Earth is in its closest position to the Sun, the Suns gravitational pull has a direct effect on the Earths orbital speed. Since the speed of an object has an effect on time. Would the increase in speed affect time in general. Of course the time is...

Homework Statement While driving north at 25 during a rainstorm you notice that the rain makes an angle of 38 with the vertical. While driving back home moments later at the same speed but in the opposite direction, you see that the rain is falling straight down. a)From these observations...

A river flows east to west at 3.0 m/s and is 80 m wide. A boat, capable of moving at 4.0 m/s, crosses in two different ways. (a) Find the time to cross if the boat is pointed directly north and moves at an angle downstream. (b) Find the time to cross if the boat is pointed at an angle upstream

Homework Statement A shortstop running at 2.0m/s toward third base catches and throws a ball toward home plate at 35m/s. IF the shortstop and catcher are lined up in a direct line of when the shortstop throws the ball, a)at what angle to his body should he throw in order for the ball to...

Homework Statement A man can row a boat at 4 m/s in still water. The current in a river is 2 m/s. The river is 40 m wide. If he wants to cross the river in the smallest possible time at what direction should he aim the boat? Given: V[B,E] = 4m/s V[W,E] = 2 m/s Down is negative. Homework...

Homework Statement The relative population of two atomic population states in equilibrium is given by Boltzmann Distribution: n1/n0 (proportional to) e^(-ε/(κT)) , where ε is the energy difference between the two states, T is the temperature and κ is the Boltzmann constant = (1.38 x...

Homework Statement A canoe has a velocity of 0.470m/s southeast relative to the earth. The canoe is on a river that is flowing at 0.490 m/s east relative to the earth.Find the magnitude of the velocity Vc/r of the canoe relative to the river. there is a graph: Vr/e pointed directly on the...

I understand the concepts behind SR and Lorentz transformations and was explaining the basics to my son by illustrating the classic laser-beam-in-a-train-car explanation. But then I started thinking... If I was in a boxcar w/ a clear wall and was throwing a ball straight up, measuring the time...

Not sure if this belongs in the SR forum, but here goes. I understand the concepts behind SR and Lorentz transformations and was explaining the the basics to my son by illustrating the classic laser-beam-in-a-train-car explanation. But then I started thinking... If I was in a boxcar w/ a...

Homework Statement A missile is launched from a fighter jet cruising horizontally at a speed of 280 m/s, at an altitude of 1800 m. The initial velocity of the missile relative to the fighter jet is 160 m/s, in the forward direction. The missile is powered by its own engine, which provides it...

Relative energy of simple 2 particle system (confused!) Ok so I have a simple question which I feel I should know the answer to: Setup: Two particles of different mass.. say M and m (where M > m) are moving past each other by some constant velocity. If we view the energy of the system from...

Homework Statement Car A is traveling east at 20m/s toward the intersection, car B from rest 40 m North of the intersection and moves south steadily gaining speed at 2.0 m/s^2. six second after A crosses the intersection find 1) position of B relative to A 2) the velocity of B relative to A...

Homework Statement Two airplanes taxi as they approach the terminal. Plane 1 taxies with a speed of 11 m/s due north. Plane 2 taxies with a speed of 8.5 m/s in a direction 20 degrees north of west. a) What is the magnitude of the velocity of plane 1 relative to plane 2? b) What is the...

Dynamics Help Needed! Relative velocities problem Homework Statement see link: http://www.flickr.com/photos/55153239@N03/6199846646/ Homework Equations Can you please help me solve this problem? I have 3 unknowns: Va, Vb, and Thetha; but only two equations Vb(cos(theta)) -...

Homework Statement A Boeing is flying east at 150 km/hr, After 2 hours it is 350 km East and 74 km south of its starting point. What is the magnitude and direction of the wind velocity? Homework Equations Not sure if anyThe Attempt at a Solution Well I really had no idea what to do so i...

Homework Statement A helicopter velocity relative to the ground is flying south for exactly .75hours. A wind blows and the helicopter ends up 30 Km in a southwesterly position away from her starting point. the helicopter speed relative to the ground is 50km/hour. What is the direction and...

if a rocketship in space is approaching the speed of light and its relative mass is increasing then i assume the fuel mass is increasing which would make it more potent the closer the ship gets to the speed of light which would give it infinite force when the ship reaches the speed of light...

Homework Statement http://imgur.com/EcjIaHomework Equations I already got the first part (v_b/a) i need to find r dot and theta dotThe Attempt at a Solution well i got v_b/a. for r I was thinking of using sqrt(y^2 +x^2) at the r and taking derivatives of that. i don't quite understand polar...

Homework Statement 1) A boy is floating on a raft in a river. THe water flows at a speed of 12m/s east. The boy's feet kick the water,causing a velocity of 2m/s at an angle of 43 degrees north of east. Using Vector components, calculate the magnitude of the raft's velocity. 2)One vector...

Homework Statement A plane traveling horizontally to the right at 100 m/s flies past a helicopter that is going straight up at 20 at 20 m/s. From the helicopter's perspective, the plane's direction and speed are: a) Right and up, less than 100 m/s. b) Right and up, 100 m/s. c) Right and...

A swimmer crossing a river proceeds at an absolute speed of 2.5 m/s on a course oriented at a 45degree angle to the 1 m/s current. Given that the absolute velocity of the swimmer is equal to the vector sum of the velocity of the current and the velocity of the swimmer with respect to the current...

Homework Statement (In textbook, given a figure, I cannot redraw that figure in this applet, so I shall describe the question in words) I am given a rectangular xy coordinate system determined by the unit basis vectors i and j and an x'y'-coordinate system determined by unit basis...

A swimmer who achieves a speed of 0.75 m/s in still water swims directly across a river 72 m wide. The swimmer lands on the far shore at a position 54 m downstream from the starting point. (a) Determine the speed of the river current. (b) Determine the swimmer?s velocity relative to the shore...

Homework Statement Person X jumps off a cliff from a height of h to the ground. On the way down X fires off a boaster which has a positive acceleration compared to gravity. Find in terms of t(time in seconds), mass, and gravityHomework Equations x=x0+(vt^2)+1/2(at^2) F=maThe Attempt at a...