Answer:
Explanation:
Using the below formula
Speed of sound = ( distance between observers) *2/(total time taken)
Now putt the given values ,
time taken = 0.80 sec
distance = 256 m
hence
V of sound= 256*2/0.80
V of sound = 640 m/sec
Explanation:
Below is an attachment containing the solution.
Answer:4
Explanation:
Given
Frequency of beats is 3 beats per second
Frequency of first tuning fork is 
Beat frequency is difference in the frequency of tuning forks i.e.
either
or 
so 
or

so there is not enough information given to decide.
Answer:
(a). The angle of refraction is 19.26°.
(b). That is proved that the rays in air on either side of the glass are parallel to each other
Explanation:
Given that,
Angle of incidence = 30.0°
Index of reflection of glass = 1.52
(a). We need to calculate the angle of refraction for the ray inside the glass
Using snell's law


Put the value into the formula



(b). We know that,
The incident ray and emerging ray is equal then the ray will be parallel.
We need to prove that the rays in air on either side of the glass are parallel to each other
Using formula for emerging ray


Put the value into the formula



So, 
This is proved.
Hence, (a). The angle of refraction is 19.26°.
(b). That is proved that the rays in air on either side of the glass are parallel to each other
Well, you should TAKE COVER UNDER A STUDY DESK, TABLE OR AGAINST AN INSIDE WALL. Which is C. This is because, doing this protects you from the falling objects. If you do A or B, you will probably get crushed by falling objects because you are exposed. Hope I helped.