Earthquake engineering
two harmonic displacement waves
both with unit amplitude
first wave has wavelength = 10 m and period = 1 s
second wave has wavelength = 11 m and period = 1.1 s
plot the variation with distance for the first 300 m induced by the superposition of the two waves 2 s after the initiation of the motion
determine the wavelength of the apparent wave from this plot.

Electric field of the earth. the earth has a net electric charge that causes a field at points near its surface equal to 150 n> c and directed in toward the center of the earth. (a) what magnitude and sign of charge would a 60-kg human have to acquire to overcome his or her weight by the force exerted by the earth’s electric field? (b) what would be the force of repulsion between two people each with the charge calculated in part (a) and separated by a distance of 100 m? is use of the earth’s electric field a feasible means of flight? why or why not?

Point charges q1=+2.00μc and q2=−2.00μc are placed at adjacent corners of a square for which the length of each side is 1.50 cm . point a is at the center of the square, and point b is at the empty corner closest to q2. take the electric potential to be zero at a distance far from both charges. part a what is the electric potential at point a due to q1 and q2? express your answer with the appropriate units.

Estimate of the number of stars in our galaxy