Xét một solenoid có chiều dài rất lớn so với bề ngang. Trong số các cách dưới đây thì cách nào là hiệu quả nhất để tăng từ trường bên trong solenoid?

What do you need on

W= fd
where f is an applied force and d is the distance over which it is applied. when a parachuting skydiver is at constant velocity, he is experiencing "terminal velocity", the point at which his acceleration down is canceled out by air resistance. that means that the resisting force of the air is equal to his weight, but in the opposite direction. with this, we can solve for the work done by the force.
w = fd
w = (92.0)(9.81 m/s^2) (325)
w= 2.93 x 10^5 j
the value for work in this case is positive because it is pushing up on the skydiver, who has a downward force of gravity.
therefore the answer is 2.93 x 10^5 j

It really doesn't matter for any of the questions that you've listed.

B) erini just took the test and it is correct