It really doesn't matter how long the flight of stairs is. What we really need to know is how much height Mary gained, straight up. We don't know that. If we knew the height then the total amount of work she did would be 87 x the height in meters. The unit is joules. Then the power she delivered would be that number divided by the six seconds and that unit is watts.
By the way ... it's troubling that Mary's weight is only about 20 pounds. It's doubtful that such a tiny creature could run up a flight of stairs.
Answer: Ok, first lest see out problem.
It says it's a Long cylindrical charge distribution, So you can ignore the border effects on the ends of the cylinder.
Also by the gauss law we know that E¨*2*pi*r*L = Q/ε0
where Q is the total charge inside our gaussian surface, that will be a cylinder of radius r and heaight L.
So Q= rho*volume= pi*r*r*L*rho
so replacing : E = (1/2)*r*rho/ε0
you may ask, ¿why dont use R on the solution?
since you are calculating the field inside the cylinder, and the charge density is uniform inside of it, you don't see the charge that is outside, and in your calculation actuali doesn't matter how much charge is outside your gaussian surface, so R does not have an effect on the calculation.
R would matter if in the problem they give you the total charge of the cylinder, so when you only have the charge of a smaller r radius cylinder, you will have a relation between r and R that describes how much charge density you are enclosing.
Magnetism.
HOPE THIS HELPS !
The size of the forces between you and the planet you're on is
your weight on that planet.
Don't forget that you pull the planet with a force equal to the force
that the planet pulls on you. Your weight on Earth is the same as
the Earth's weight on you !
The added weight of the sand puts more downward pressure on the wheels contacting the rails, which would cause the trains speed to decrease.
