Answer:

Explanation:
Given:
- wavelength of light in the air,

- time taken to travel from the source to the photocell via air,

- time taken to reach the photocell via air and glass slab,

- thickness of the glass slab,

<u>Now we have the relation for time:</u>

hence,

c= speed of light in air



For the case when glass slab is inserted between the path of light:
(since light travel with the speed c only in the air)
here:
v = speed of light in the glass


Using Snell's law:



You can't change time to a measurement of distance
The centripetal acceleration is given by

where v is the tangential speed and r the radius of the circular orbit.
For the car in this problem,

and r=40 m, so we can re-arrange the previous equation to find the velocity of the car: