Answer: Larmor suggested in 1919 that a self-exciting dynamo could explain the magnetic field of the earth, as well as that of the sun and other stars, but it was Elsasser and Bullard in the 1940s who showed how motion in the liquid core of the earth might produce a self-sustaining magnetic field. By this time seismology and other studies had given a clearer picture of the earth, as having a solid inner core, a liquid outer core, both with a composition more of metal (mainly iron) than rock, and a rocky mantle, all below a thin crust that is all we can directly see. Energy from radioactivity travels outwards as heat, producing thermal convection in the core. It seems that this convection is the cause of the earth's magnetic field, although our knowledge of the core and its dynamics is sketchy. Our knowledge is limited to saying that flow regimes like those that may be occurring in the core can produce self-sustaining dynamos, with characteristics similar to that needed to produce the earth’s magnetic field.
Explanation:
Answer:
P = 11666.6 W
Explanation:
Given that,
Work done by the motor, W = 3500 kJ
Time, t = 5 min = 300 s
We need to find the power developed by the motor. Power developed is given by :
So, the required power is 11666.6 W.
Are you familiar with any basic calculus? If so, we can just look at this derivative and see what's happening with our units here..
Here it shows that acceleration is the derivative of velocity with respect to time. In other words, we can say that:
We can read that equation as: "acceleration is the change of velocity divided by the change in time (aka the time interval)."
If you're not familiar with calculus, we can use a simple equation of motion:
where:
vf = final velocity
vi = initial velocity
a = acceleration
t = observed time interval
We can rearrange this equation to find:
This is the same exact thing we wrote before!
Picking up a box, pushing a box along the ground, and pulling a box along the ground (B, C, and D) definitely involve work being done.
If a person CARRIES a box from one place to another, AND keeps it at the same height during the entire carry, then no work is done. ( A )
