39.

(a) We use ∆x = v

avg

t = vt/2:

v =

2∆x

t

=

2(2.0

× 10

−2

m)

1.5

× 10

−8

s

= 2.7

× 10

6

m/s .

(b) We use ∆x =

1
2

at

2

and E = F/e = ma/e:

E =

ma

e

=

2∆xm

et

2

=

2(2.0

× 10

−2

m)(9.11

× 10

−31

kg)

(1.60

× 10

−19

C)(1.5

× 10

−8

s)

2

= 1.0

× 10

3

N/C .