PHYSIC

1. What is the orientation of the rod? Is there any diagram given?
If there is no induced emf, then the rod needs to be oriented vertically.
In that case, the rod doesn't cut any magnetic field lines when it is pulled vertically. Emf is induced whenever there is cutting of magnetic field lines by the rod.

2. Your answer is right.
At the highest point, the potentialy energy is clearly maximum. This makes the kinetic energy the minium, because the sum of potential and kinetic energies is a constant.


2010-04-05 23:49:35 補充：
KE is definitely NOT zero. If KE were zero, the golf ball would drop VERTICALLY DOWN suddenly when reaching the highest point. Have you ever observed such trajectory in a golf ball shot?

2010-04-05 23:51:03 補充：
Just supplement to the above answer, at the highest point, the golf ball still possesses a horizontal velocity, As such, its KE is NOT zero.

2010-04-05 23:53:11 補充：
By background radiation, we usually mean radiation coming from the "natural environment". Electrical appliances are not in existence naturally, thus they are not counted as sources of background radiation.

2010-04-05 23:54:22 補充：
Natural substances that contain natural radionuclides will emit (ionizing) radiation.

if the golf ball is a vertical motion then KE will be zero
but it is trivial that golf ball travel in air is in projectile motion,which is vertical speed is zero but horizontal speed is not zero at the highest point