39) 1/4
41a) 7.49 x 106 m/s
41b) acceleration caused by the electric field is 2.60 x 1014 times larger than acceleration caused by gravity
52) 5.08 m
53) fraction lost = 2.9 x 10-10
54) 1.02 x 10-7 N/C up
55) -6.8 x 105 C
56a) 2.6 x 1013 m/s2 up
56b) 1.4 x 1010 m/s2 down
56c) electron: 2.7 x 1012; proton: 1.5 x 109
65) 5 x 10-9 C, about 3 billion electrons
68) 1.06 x 107 N/C