# Search results

1. ### Pascual Jordan - The Forgotten QFT Physicist?

Hi, I think he tends to be mentioned whenever authors give an overview of the history. As an example, the only two QM textbooks I have available right now, Sakurai's (standard) book and Weinberg's "Lectures on quantum mechanics", do mention him and his role when it came to matrix mechanics...
2. ### Basic Physics Question-But I'm stuck!

Maybe I am reading this completely wrong then? "A certain automobile manufacturer claims that its deluxe sports car will accelerate from rest to a speed of 44.5 m/s in 8.90 s." To me, that certainly sounds like the car travels at 0 m/s in the beginning, and at 44.5 m/s after 8.90 s.
3. ### Basic Physics Question-But I'm stuck!

Your numbers are slightly off (even for what you are doing), but my main objection is this: the question tells you that the car accelerates from rest with the same acceleration all the time - yet you claim that it will travel slower after 10 seconds than it did after 8.9 seconds.
4. ### Basic Physics Question-But I'm stuck!

Well, without giving it all away, do you think that is a reasonable answer? (As you have stated the question, it is not.)
5. ### Expansion of copper

OK. Well, if it makes you feel better, those values (assuming you give α in the usual units) and the linear expansion formula does give me the same answer. Basically, thermal expansion is a small effect, which thus mainly matters for larger things.

7. ### REAL QUICK question about how to solve for the period of a simple pendulum?

What are the units of the length and for g?
8. ### Variation of pressure with depth

Yes, that's right. \Delta x only depends on \rho g h (and vice versa). By the way, this is why we often call this pressure (i.e. absolute pressure minus atmospheric pressure) gauge pressure.
9. ### Variation of pressure with depth

The piston moves due to a change in the pressure, doesn't it? So, above surface the pressure is already P_0, which corresponds to a certain compression x_0. Under the surface your equation holds and gives a compression x(P)=x_0+\Delta x. What is \Delta x?
10. ### Need to find distance of an object over an incline plane

Indeed. So, at which height y (measured vertically, not up the incline) does it stop rising?
11. ### Need to find distance of an object over an incline plane

Since there is no friction, think of why the object would come to a stop.
12. ### Positive or negative work done

It depends in which order you take the points in the potential difference. V(2)-V(1) would be the difference in energy if you go from point two to point one, while you consider the opposite path and thus gets the opposite sign.
13. ### FreeFall motion Assumptions in proving

One of them, certainly. The initial velocity is already known though, as it is given in the problem description.
14. ### FreeFall motion Assumptions in proving

My point is the equaton y_1=y_2 does not tell you at which height they collide. It does, however, provide some other useful information.
15. ### FreeFall motion Assumptions in proving

I mean, in which direction does the y axis point? Does it point upward? I.e. does higher positions correspond to higher values of y? Because, in that case the formula the gravitational acceleration is opposite to the y axis, and the acceleration a=-g. You would then have y_1 = ut -...
16. ### FreeFall motion Assumptions in proving

Can you show us what you have done so far? And which way is your coordinate axis pointing?
17. ### The Physics Behind a Bullet Hitting The Human Body

Yes, you do have momentum conservation. Sorry, what do you mean? The momentum is certainly imparted to the shot person through a force, but you don't know either the magnitude of the force or the duration of time it acts on the person, do you?
18. ### Two small beads having positive charges 3q and q are fixed

That's basically the reason, yes. In the stable case, the force will push it back towards the equilibrium, and not away from it. Another way to think about it is that the force on the particle is related to a potential through \mathbf{F} = - \nabla V \left( x \right). If the equilibrium...
19. ### Find the distance

Well, the wind is moving the air the sky diver falls through. Does this affect the motion of the sky diver or not? (Hint: think about something light, like a piece of paper or a balloon.) As for the other question, you are probably expected to use the same wind speed at all heights. That's...
20. ### Underdamped harmonic oscillator with a sinusoidal driving force

The clue is pretty much in "differential calculus". What tool have you learnt in calculus for finding the maximum of a function?
21. ### Help with physics homework

I think it would be useful if you provided more details about your attempt. For starters, what does the free body diagram look like?
22. ### Vector A has y-component Ay= +12.0 . A makes an angle of 32.0

You draw it, and then use trigonometry. (Always draw the problem!) Because you have learnt about decomposition about vectors into components, right? This is more or less the same problem.
23. ### The velocity of a particle at the origin.

There is an easier way to solve it, just factor out one of the t's: x=ct^2+bt = t(ct+b), for which x=0 when t=0 or t=-b/c. Both solutions are of course valid (based on the problem text), even if the homework website doesn't think so...
24. ### The velocity of a particle at the origin.

I guess they mean the origin of the coordinate system, i.e. x=0. You usually say t=0 rather than the slightly ominous "the origin of time".
25. ### Calculating Amplitude of Transverse Wave

Well, you have two conditions at the origin, don't you? Try using both of them.
26. ### Calculating the decrease in kinetic energy of an object as it moves against a spring

Use energy conservation. The loss in kinetic energy corresponds to an increase in the potential energy due to the spring.
27. ### The velocity of a particle at the origin.

Maybe they're looking for the velocity at the other time the particle is at the origin?
28. ### Acceleration of Gravity

Well, let us take this carefully. 1. The ball loses speed as it moves up. Thus the acceleration is in the opposite direction of the velocity, i.e. downwards. (Think of it as vectors.) 2. The ball reaches a max height, where it has a minimum speed of zero. The acceleration continues to point in...
29. ### Acceleration of Gravity

OK, suppose you throw a ball up in the air. Is the sign of the acceleration negative while it is moving upwards and positive when it is moving downwards then?
30. ### Acceleration of Gravity

In which direction is the acceleration?