Asatellite of mass m moves in a circular orbit of radius r at a constant speed v around the earth which has mass me. now, my question is: why is b) correct? b) the net work done on the satellite by gravity in one revolution is zero.

-- "Work" is the product of (force exerted on the object) x (distance the object moves in the direction of the force).

Since the orbit is a circle, the gravitational force toward the center is always perpendicular to the orbit.  The object never moves in the direction of the force.  If it did, it wouldn't be 'R' away from the center of the circle.

So the product of (gravitational force) x (distance in the direction of the force) is always zero.

-- Even if the orbit ISN't a circle . . . there are some parts of the orbit that aren't quite perpendicular to the gravitational force.  If the satellite is traveling through one of those parts AND getting closer to the central body, then gravity is doing positive work on the satellite.  If the satellite is traveling through one of those parts and getting FARTHER from the central body, then the satellite is the one doing positive work, and gravity is doing 'negative work'.  The work done by gravity ... and the work done by the satellite ... is zero over a complete revolution, although not zero at every point.

This is exactly the definition of a "Conservative Force" ... a force that does zero work through one trip around any CLOSED path.  Gravity is a conservative force, and so is the Electrostatic force.

a solenoid is created by wrapping a l = 90 m long wire around a hollow tube of diameter d = 4.5 cm.   the wire diameter is d = 0.9 mm.   the solenoid wire is then connected to a power supply so that a current of i = 9 a flows through the wire.

randomized variablesl = 90 m

d = 4.5 cm

d = 0.9 mm

i = 9 a                                          

write an expression for the number of turns, n, in the solenoid. you do not need to take into account the diameter of the wire in this calculation.

calculate the number of turns, n, in the solenoid.

write an expression for the length of the solenoid (l2) in terms of the diameter of the hollow tube d.

calculate the length of the solenoid (l2)   in meters.

calculate the magnitude of the magnetic field at the center of the solenoid in teslas.

explanation:

this is an example of "committed" time.

committed time, as contracted time, takes need over essential and available time since it is seen as profitable work. it alludes to the time allotted to keep up a home and family. at the point when a man is commuting using committed time this individual may feel that the drive is an obligation to family, for example, strolling youngsters to class or driving a mate to work. contracted and committed time clients may feel that their commute could really compare to the commute of important or leisure time clients on the grounds that their commute is profitable work. in this manner, they might be more disposed to pick a mechanized method of movement.