Thursday
June 20, 2013

# Homework Help: physics (for bobpursley, or anyone)

Posted by mike on Thursday, May 10, 2007 at 6:40pm.

Hey bob, its Mike and Jake. We wanted to start over on a new foot with you.
We got assignment worth over 300pts, so far we getting 80% of the questions right, which is pretty good.

We are stuck on some questions. We will tell you the questions and tell you what we think and you tell us whatever can help steer us in the right direction if we are wrong.

Deal?

1) An electron is placed at a certain point in space and it instantly begins to move away, however, a neutron placed at the same point does not move away. What kind of field must be present at that point in space?

An electron is charged and a neutron is not. So a magnetic field and electric field would have to be in place right? Those fields affect charges. Jake says we have to think about a gravitational field. I know that it affects all things, but the neutron is not moving. So would there still be a gravity field no matte what?

2) Which of the following constitutes a very high efficiency for a useful, working heat engine?
1. 200%, 2. 150%, 3. 50%, 4. 100%
In the book we have it says heat engines are always less than 100% efficient. So that would mean it would be 50%. Jake is confused about this, he thinks it should be 100%.

3) Velma is riding on the back of a turtle, which moves 1 cm per second with respect to Mort who is standing near by. Whose time is slowed down?
We think Velma says Mort's time is slower, and Mort says Velma's time is slower.
This is because of time dilation, right?

thanks again.

1) In space, assume gravity is zilch. Magnetic fields do not affect charges unless they are moving. The force on the charge is prop to speed, so forget the magnetic field.
2) Look at practical inlet and exhause temps. Say in a boiler 3500K is the fire temp, and the outlet temp is 350K

What does the Carnot efficiency? Practially, because of heat losses, it is half this in a very high efficent power boiler.

3) The object moving time is slowed with respect to the stationary object.

1) Yes, there must be an electric field. A gravitational field would cause the neutron and the electron to accelerate equally fast. There can still be a gravitational field provided it is weak enough for the acceleration of the neutron to have gone unnoticed.

Also note that a magnetic field cannot cause a charge to accelerate when its velocity is zero.

Although the neutron is neutral, it is composed of charged particles: quarks. In a very strong electric field a dipole moment will be induced. If the electric field is not uniform then that will cause a force to be exerted on the neutron. But this can only be a very small effect in practice.

Also, even in the absense of an electric field the neutron has a dipole moment (a permanent dipole moment), but this so small that it hasn't been experimentally detected yet. We know that it must exist because of a fundamental asymmetry in the laws of physics.

No one has answered this question yet.

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