[Chemistry4me (OP)]

I think my head just exploded after all of that.

[lyner]

As we've assumed the current yo be 1A, the value of R is 7.2 ohms.

[Chemistry4me (OP)]

Didn't we already know that R was 7.2 ohms?

[lightarrow]

The exact value of Q = (1/R)√(L/C) is 5/4 (see post up).

[syhprum]

How can we include √(L/C) in our calculations when we are told nothing about them ?.
We are told nothing about the value of R we can only assume a convinient value.
In my opinion the only information we can derive from the data given is the Q factor (1.25) and the phase angle of the current (53.13°).

[lightarrow]

How can we include √(L/C) in our calculations when we are told nothing about them ?.

Not understood this one.

We are told nothing about the value of R we can only assume a convinient value.
In my opinion the only information we can derive from the data given is the Q factor (1.25) and the phase angle of the current (53.13°).

Exactly. We have 3 equations and 4 unknown. Solved them we have the parameters I wrote, from which we can only find what you said.

[Chemistry4me (OP)]

Why does E_k = 0.5mv² but E = mc²
How are the two equations related? What happened to the 'm'?

[syhprum]

E=mc^2 is derived from geometric considerations and is relevent as velocities approach c E=0.5*mv^2 belongs to the world before Einstein and Lorentz and does not take into account the changes that take place in M as the velocity increases.

[lightarrow]

Why does E_k = 0.5mv² but E = mc²

They are both false []

How are the two equations related? What happened to the 'm'?

E_k = 0.5mv² is valid only for bodies with non zero mass and at non relativistic speeds; E = mc² is valid only at zero speed.
The correct one, valid for all speeds and with massive or non-massive bodies (in special relativity) is:

E² = (cp)² + (mc²)²

where p = momentum. If m = 0 (photons, gluons, ecc.) then E = cp. At zero velocity p = 0 so E = mc².

Kinetic energy is total energy minus rest energy:

E_k = E - mc²

[lyner]

How can we include √(L/C) in our calculations when we are told nothing about them ?.

Not understood this one.

We are told nothing about the value of R we can only assume a convinient value.
In my opinion the only information we can derive from the data given is the Q factor (1.25) and the phase angle of the current (53.13°).

Exactly. We have 3 equations and 4 unknown. Solved them we have the parameters I wrote, from which we can only find what you said.

Yes - the circuit can be scaled up or down in Impedance, according to taste and availability of components. It's just the ratios that count.

[Chemistry4me (OP)]

E_k = 0.5mv² is valid only for bodies with non zero mass and at non relativistic speeds; E = mc² is valid only at zero speed.
The correct one, valid for all speeds and with massive or non-massive bodies (in special relativity) is:

E² = (cp)² + (mc²)²

where p = momentum. If m = 0 (photons, gluons, ecc.) then E = cp. At zero velocity p = 0 so E = mc².

Kinetic energy is total energy minus rest energy:

E_k = E - mc²

Ooh  [] (showing my ignorance here) That's a new one! I must really remember that.

[Chemistry4me (OP)]

This question has me scratching my head, I can't seem to get the 'correct' answer. [:I] [] Maybe I'm not understanding something. It goes something like this: A uniform beam 2.0 metres long is known to weigh between 400 N and 500 N. Using a spring scale, S and a pivot block, P, an experiment was made with the beam balanced horizontally on P and S to enable the weight to be calculated. The spring scale reads 85 N when P is 0.75 m from one end, what is the weight of the beam?