A long plank XY lies on the ground. A load of 120N is placed on it, at a distance of 0.50 m from end X as shown. End Y is lifted off the ground. The upward force to do this is 65N.

In the diagram, W is the weight of the plank, acting at its mid-point.
What is the value of W?
A 35N
B 47N
C 100N
D 133N

Certain bacteria (such as aquaspirillum magnetotacticum) tend to swim toward the earth’s geographic north pole because they contain tiny particles, called magnetosomes, that are sensitive to a magnetic field. if a transmission line carrying 100 a is laid underwater, at what range of distances would the magnetic field from this line be great enough to interfere with the migration of these bacteria? (assume that a field less than 5% of the earth’s field would have little effect on the bacteria. take the earth’s field to be 5.0 * 10-5 t, and ignore the effects of the seawater.)