I've decided to try my hand at creating youtube videos and I'd like to know what fellow PF members think. This is a community whose opinions I value.
The video can basically be divided into 6 slides (about 18 minutes long in total)
1) Definition of relative velocity (verbally)
2) Definition of...
Two students run around a 400m sport field. A goes anticlockwise (i.e., 1-2-3-4-1) while Bruns clockwise (i.e., 1-4-3-2-1). Students A and B can run 400 m in 75.0 s and 65.0 s,respectively.
Students A and B should meet at some point of the run. Where do they meet? Assume the cross-over...
is it possible?
I've given it quite some thought, and my conclusion was that it would be possible, cuz right after I jump, I'll still have the same velocity in the same direction as the running train?
In the question I assumed the velocity of the circular object to be :
$$\vec v_A= v cos( \phi + \omega t) \hat i + v sin(\phi + \omega t) \hat j$$
where $$\omega = \frac{v}{R}$$
Velocity of the other particle is
$$\vec v_B = v \hat i$$
Now magnitude of relative velocity comes out on...
How is it possible that Earth's rotation doesn't affect our relative velocity? In other words, if I walk in the opposite direction of Earth's rotation, shouldn't I reach destinations faster than if I walk in the same direction?
Sorry if the terms are not that accurate, I’m an architect!
Hi everyone,
I was looking to develop my physical insight when I encountered this book by Lewis Caroll Epstein. For the crosswind problem, I couldn't understand the author's explanation; in particular, his concept of "artificial wind," and the force being larger in this case than the previous...
For some reason I'm having trouble understanding relative velocity problems. I know how to solve this, but I keep guessing at random methods until my answer matches the solution in the textbook.
I solved it correctly by breaking the velocity of the ball into x- and y- components, then solved...
The official solution says ±25.4°, but I'm having trouble reproducing it. Here is my solution:
1) The components of the velocity of firework F with respect to the ground G in the moment of explosion are the following (Notice, I'm using sin, because the statement says 30.0° from vertical.)...
I was able to solve this question successfully by utilizing the sine and cosine law however my instructor said I was only allowed to utilize the vector component method, I am unsure how to complete this question using the vector component method as we have two unknowns(those being the angle of...
So far I have this:
vbwx= 4.40c0s(28) = 3.88496409
vbwy= 4.40sin28 = 2.065674876
vpwx= 4.4ocos28
vpwy= 4.40sin28 +2.02
Find Square root of vpx^2 + vpy^2 = 5.43?
Im confused as to whether we add the 2.02 to the sin28 or the cos28 though, did I do it right? Also, not sure how to find the...
vcanoe_wrt_ground = 3 m/s + (-6) m/s = 3 m/s - 6 m/s = -3 m/s
Thus, if I understand this correctly, the rower will never reach his goal 36 m away as his canoe's resultant velocity is negative (i.e., his canoe is effectively going downstream even though it is trying to go upstream). My only...
I'm trying to understand this paper (equation 2.16 specifically):
Bini, D., Carini, P., & Jantzen, R. T. (1995). Relative observer kinematics in general relativity. Classical and Quantum Gravity. Am I correct in reading there is no way to express the relativistic relative velocity composition...
I can solve this question using relative Velocity or using 2 kinematics equations. But a peer of mine, tried to do it in a different way. He substituted the above said values in the 4 equations and solved for u in terms of t and differentiated them and equated to to 0 to find a maxima. He found...
The question I have is that if the aero plane is traveling in the same direction as the wind, would it not increase its velocity, as in with boats and streams? So, if by chance, ##w = v##, then the velocity of the aero plane would double. It feels weird as going by the same logic, if the speed...
Where exactly have I gone wrong? I think it is the part where I assume that the person gains the deceleration of the car, but I have no other way to proceed in this case. Also please only use the equations that I have posted below, and it would help if you would not use the equation for...
Here's what I did so far.
The velocity of the first car is ##v = v_0 +at##
Frame of reference S = the road
Frame of reference S' = the second car
thus, v' is the speed of the first car in the frame of reference S' and v the speed in the frame of reference S.
Here's what make me doubt.
The...
Summary:: I would like to calculate the Doppler shift for a signal sent by a moving ship to a moving satellite.
I want to calculate the frequency observed by an LEO satellite when a signal is transmitted from a moving ship. The LEO satellite has a velocity of 7120m/s and orbits at a height of...
Problem : The statement is given above. Here I attach the image of the problem to the right.
Attempt :
(1) Condition for collision : For the two particles to collide, there should be no relative velocity perpendicular to their "separation vector" ##\boldsymbol{s}##. Hence, we must have ...
Problem statement : While the statement is given above, I draw the given image for the problem.
Attempt : It is clear at the outset that, since the velocity of river is constant, the man will not take the same time for the forward and reverse journeys. For both journeys however, the Relevant...
The point of confusion is deciding the direction each persons sets out in i.e. velocity direction of each person. Knowing this will probably help in getting the solution.
At t=0, I can say that velocity of each person is as shown in diagram below.
Heres how I tried to set up the problem.
I took the laboratory to be S and the frame of the particle whose speed we know to be S', so that the speed of S' relative to S is u = 0.65c.
Also, by convention, S' moves to the right of S, so that S moves to the left of S'.
Next, we know that the...
So I've managed to confuse myself on this problem :)
Since the problem says we can assume ##m_p << m_b##, I'm assuming that the velocity of the bowling ball will be unchanged, such that ##\vec v_{b,i} = \vec v_{b,f} = -v_{b,0} \hat i##
I started out using the energy-momentum principle, ##(\vec...
Could I please ask for any help with the following question:
Here's my attempt: (i and j are unit vectors in the directions of east and north respectively)
(apologies that LaTeX is simply not working for me, I'll label the angles in each case T and P as shown in my diagram)
Let the...
Please can I ask for help with the following as to where I'm going wrong.
Book answer is 20 knots and 315 degrees
My solution:
In the below diagram I have sketched the two situations, k is the true speed of the wind.
First question is, is my diagram correct?
The velocity of the wind...
Here it is given that the flag flutters in the direction of wind w.r.t. to man. But why would the direction of fluttering of flag would change without any tangential acceleration. Is there a pseudo force acting on it. I think the direction if fluttering should remain same.
Wikipedia gives, "The relative velocity ##{\displaystyle {\vec {v}}_{B\mid A}}## is the velocity of an object or observer B in the rest frame of another object or observer A."
Suppose the coordinate system being used in the rest frame of ##A## is has its origin slightly displaced from ##A##...
(pw is person to water, pf is person to ferry, fw is ferry to water)
I get Vpw = Vpf + Vfw. Therefore Vfw = Vpw + Vpf, which is
Vfw = -Vwp + Vpf. I also have that the x component of Vpw is negative.
I think I'm getting confused with either the order of the formula or the negative negatives (or...
Hi all,
Not sure on how to start this question in the first place, but from what I gathered from the data given
I managed to derive this from the question:
##\theta = 53.13\deg##
Let inside truck be t, final position be f, and ground be g
##D_{ft} = L##
##D_{fg} = xL##
Also, for velocity...
There have been some other threads on similar problems but none address one specific point I'm confused about.
The change in GPE of a body is the negative of the work done on that body by a gravitational field between two points; by this logic, since the same (but opposite) gravitational forces...
The answers were
1) 150 km/h
2) 200 km/h
3 )500 km/h
4) 700 km/h
5) 800 km/h (Chosen Solution)
I know that values 700km/h ,100km/h ,-100km/h are possible scenarios but in what ways are 150km/h ,200km/h and 500km/h possible ?
When only force acting on body is a central force, angular momentum is constant and given by:
L = mr^2 * w
where r is distance from origin, and w is angular velocity.
Angular momentum can also be written as following:
L = r x mv = rmv * sin(theta) where v is tangential velocity, which is...
Unable to understand why this is the case?
Also, if it were in two dimensions then I am guessing the same would apply, only the 'x-co-ordinates' and 'y-coordinates' would add up separately?
Lastly, does the same hold for acceleration.
I am aware that this is a trivial question, many books...
So I was just wondering if someone could check my method for (b) as sometimes I can have a tendency of getting the relative components wrong ect.
Diagram 1
(a)
Time for PY: ##T=L/c##
Time for YP: ##T=L/c##
Total Time:##2L/c##
(b)
Velocity for PY: ##c-v##...
for part 1: t= d/s = 9000/13 = 692.31s
for part 2: What i am unsure about is wether or not this is after the initial observation or exactly what they are asking honestly. so i found the relative velocity of the bus to the car and vice vera and came up with: t=d/s = 9000/4 = 2250s however i don't...
v=16m/s+4*.659s=18.636m/s (for lift)
v0=16m/s-9.81*.659s=9.53m/s
my question is that why 16m/s is considered for screw velocity ? it is given for lift .what does it mean 9.53m/s? If you drop something , it gets acceleration and I calculate it 6.45m for screw while falling and why should I...
Homework Statement
The water in a river flows uniformly at a constant speed
of 2.50 m/s between parallel banks 80.0 m apart. You
are to deliver a package across the river, but you can
swim only at 1.50 m/s.
(c) If you choose to minimize the distance downstream
that the river carries you, in...
Homework Statement
Three particles A, B, C, are situated at the vertices of equilateral triangle of side l. They approach each other with velocity v, such that A always moves toward B, B towards C and C towards A. What will be the initial acceleration?
Homework EquationsThe Attempt at a...
This is a question about the concepts behind rigid body rotation when we use relative velocity.
In general, let us say that we have a rigid body and on it are two points, A and B, which are moving with velocities vA and vB respectively. These velocities are in random directions.
The theory...
Homework Statement
Hi, everyone. I came across a basic calculus problem concerning movement of 2 problems, I've attempted to solve it using vector analysis and got 1 answer, and then solved it with differentiation and got a different answer. I'll show a version of it I made which is a bit more...
Hi! I'm an utter novice at physics, so please bear with me if I ask a foolish question.
I just learned that velocities don't purely add: 2m/s + 2m/s does not equal 4m/s, but something like 3.9999999...9 m/s, and so on. Something to do with the upper limit of c.
Logic makes me assume that this...
This is something related to my job.
There are two components A & B both traveling the same direction but at a different velocity. I can find out the exact velocity of both the components when they just hit each other, thus relative velocity is known.
Is there a way I find out the force...
Homework Statement
Imagine we are observing two aeroplaes from the ground and let their velocities be ##\mathbf{u}## and ##\mathbf{v}## respectively. Assume that the first plane has radar equipment permitting a measurement of the speed of the other plane relative to itself. The velocity so...
Homework Statement
AB is a rod of length 10 m that is leaning against the wall. Given variables are shown in the diagram. Find angular velocity of A wrt B.
https://imgur.com/a/8bEdYhN
I have a doubt in one step that I will highlight in "The attempt at a solution" part.
Homework Equations...
Homework Statement
A man wishes to cross a river of width 120 m by a motorboat. His rowing speed in still water (or relative to water) is 3 m/s and his maximum walking speed is 1 m/s. The river flows with a velocity of 4 m/s.
(a) Find the path which he should take to reach the point directly...
Homework Statement
A river of width 4 km flows at 5 km/h. A swimmer whose speed relative to water is 4 km/h, starts swimming from a point A on a bank. What minimum distance will the swimmer have to walk on the other bank to reach point B directly opposite to A?
[/B]Homework Equations
Vba = Vb...
In this derivation of the Ideal Rocket Equation (https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation#Most_popular_derivation), they use the fact that ##V_e = V - v_e##, or that the velocity of the exhaust in the observer frame ##V_e## is the velocity of the rocket ##V## minus the speed of...
Homework Statement
A bird can fly in still air at 100km/h. The wind blows at 90km/h from W(x degrees)S. The bird wishes to return to its nest which is due E of its present position. In which direction, relative to the air, should it fly?My textbook says that the velocity of the bird relative to...
So I read these two other threads:
https://www.physicsforums.com/threads/relative-speed-of-two-cars.642873/
https://www.physicsforums.com/threads/two-cars-colliding.740948/
And gathered what I already thought was correct, that the relative velocities of two cars of equal mass crashing into...