75.

(a) We use Eq. 29-16 to calculate r:

r =

m

e

v

qB

=

(9.11

× 10

−31

kg)(0.10)(3.00

× 10

8

m/s)

(1.60

× 10

−19

C)(0.50 T)

= 3.4

× 10

−4

m .

(b) The kinetic energy, computed using the formula from Chapter 7, is

K =

1

2

m

e

v

2

=

(9.11

× 10

−31

kg)(3.0

× 10

7

m/s)

2

2(1.6

× 10

−19

J/eV)

= 2.6

× 10

3

eV .