Physics heLp anyone good????

Question

can someone help me solve this???

1. an electric field applies a force of 9.11x10^-16 N to an electron emitted from the cathode of a cathode-ray tube at essentially zero velocity. if the field force is constant, find the time required for the electron to reach the screen 20cm from the cathode. the mass of an electron is 9.11x10^-31 kg.

a. 20nsec

b.91.1nsec

c.500nsec

d.50usec

e.109usec

f.242usec

2. referring to question 1, what is the instantaneous speed of the electron 15 nsec after leaving the cathode?

a. 16,400 km/sec

b.28,300 km/sec

c.15,000 km/sec

d.61,300 km/sec

10 pointz for the best answer!thanks!^_^

Answer 1

FORCE F=9.11x10^-16 N

MASS M= 9.11x10^-31 kg

ACCELERATION A = F/M =10^15 M/SEC^2

DISTANCE S = 20 CM = 0 .2 METRES

S = UT + 0.5 A T^2

0.2 = 0 +  0.5 x 10^15 T^2

T^2 = 4 x 10^-16 SEC

TIME T = 2 x 10^-8 SEC

= 20 NANO SEC

= ANSWER (A)

2. VELOCITY V AT TIME T IS GIVEN BY

V = U + AT

AFTER 15 NANO SECOND THE VELOCITY IS GIVEN BY

V = 0 + 10^15 M/SEC^2 x 1.5 x 10^-8 SEC

= 1.5 x 10^7 M/SEC

= 1.5 x 10^4 KM/SEC

= 15000 KM/SEC

= ANSWER (C)