About how long ago was the last retreat of the glaciers from North America and Europe?
a. 60,000 years
b. 10,000 years
c. 2 million years
d. 6000 years
Question 2
Consider two charged spheres, one with charge +2 C and the other with -2 C. A proton (a positively charged particle) is at the point halfway between the spheres. What is not zero?
a. the potential energy of the proton
b. the work to move the proton from infinity to that point
c. the force on the proton
d. all of the three above are zero