# Recent content by apelling

1. ### Entery level Mass-energy equivalence questions

The increase in kinetic energy must have come from a reduction in rest mass. In other words the mass of the two alphas is less than the mass of X and the proton. You have values for the rest mass of the alphas and the proton and the mass equivalent of the kinetic energy gained.
2. ### Entery level Mass-energy equivalence questions

For question 1 find the difference between the initial kinetic energy and the final kinetic energy. Then use E=mc^2 to convert energy to a mass equivalent.
3. ### Starship special relativity problem

There is nothing wrong with this calculation. All velocities relative to the observer are below c. It appears that the projectile has a relative velocity to the station of 1.1c from the ship's view but this is ok becuase relative to the ship all velocities are less than c. The velocity of the...
4. ### Starship special relativity problem

I get -3.31s for the space station clock, not +3.31s. Is a negative or positive answer?
5. ### Entery level Mass-energy equivalence questions

The guiding principle is mass/energy conservation. initial (rest mass energy + kinetic energy)= final (rest mass energy + kinetic energy) Question 1 is just concerned with the increase of kinetic energy expressed as a mass equivalence. Question 2 just use the above equation. Be careful to...
6. ### Lorentz transformations combined with force

I would agree with what you have said. However you are perhaps expected to say something more about the cyclotron. Even at non-relativistic speeds r increases with v. However r is directly proportional to v and since time for 1 rev=2∏r/v the frequency of revolution is a constant which...
7. ### Help differentiating energy wrt time.

I was thinking L was the extension of the springs when at equilibrium and x was the displacement from equilibrium. Anyhow it does not matter much since the constants drop out during differentiation.
8. ### Proton enters magnetic field in spiral trajectory

The pitch of a spiral is the distance moved after one complete revolution. The diagram in section 2.5 of this wiki article is fairly clear:- http://en.wikipedia.org/wiki/Screw_thread The two velocity components would be vsinθ perpendicular to B vcosθ parallel to B vsinθ should be used...
9. ### Resonant frequencies in a tube with adjustable length

I think unfortunately this question as stated is meaningless. Tuning forks only make one frequency so why is the question asking about the quantity of resonant frequencies? This has misdirected your thinking. If the question actually is asking " at what lengths of tube up to 1m does...
10. ### Shortest possible period of revolution of two identical gravitating solid spheres

The 2 is correct. I got 16 because I used r=1/2 separation of masses. When cubed in the final equation this leads to a factor of 8 difference. 2 x 8 =16
11. ### Finding and labeling equilibrium points between multiple point charges.

One approach might be to make an equation for the electric potential. Because potential is a scalar this is easier than trying to find an equation for force or field strength, which would require vector addition. Now field strength is equal to -potential gradient (E=-dV/dr or more generally...
12. ### Help differentiating energy wrt time.

E = 1/2 mv^2 + k(x-l)^2 + 2k(l-x)^2 -mgx - don't think this is quite right I am guessing that we have one spring above the mass and one below? The terms for elastic spring energy are based on 1/2ke^2. Where e is spring extension. Isn't the extension of the springs l+x and l-x? Are...
13. ### Shortest possible period of revolution of two identical gravitating solid spheres

You should be using r/2 in this equation to be consistent with your definition of r.
14. ### Shortest possible period of revolution of two identical gravitating solid spheres

Are you using v^2=\frac{\pi^2 r^2}{T^2}
15. ### Mass on the wedge

I sort of agree with you but would quibble over the wording. The resultant force is always given by ma. When going up the slope a=g(sinα+μ*cosα) But when going down a=g(sinα-μ*cosα) Resultant F=ma=mg*sinα+ reaction force from plates. Reaction force from plates=±mgμ*cosα So when going...