A ray of monochromatic light having a wavelength of 4.00 x 10-7 meter in air passes from air through Lucite and then into air again.
1)Calculate the frequency of light in air.
2)Identify the color of the light.

Explanation:

wavelength of light = 4 x 10⁻⁷ m

frequency = velocity in air / 4 x 10⁻⁷

= 3 x 10⁸ / 4 x 10⁻⁷

= .75 x 10¹⁵ Hz

= 75 x 10¹³ Hz.

Wave length = 4 x 10⁻⁷ m

= 400 x 10⁻⁹m

400 nm

colour of light having this wavelength in air is violet .  

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s