Explanation:
Given that,
Frequency of train horn, f = 218 Hz
Speed of train, 
The speed of sound, V = 344 m/s (say)
The speed of the observed person, 
(a) When the train approaches you, the Doppler's effect gives the frequency as follows :

(b) When the train moves away from you, the Doppler's effect gives the frequency as follows :

Hence, this is the required solution.
 
        
             
        
        
        
I think the correct answer choice is c
        
             
        
        
        
Answer:
a)Work done by fireman=   2.15  Btu
b) Time t= 0.86 sec
Explanation:
Given that
Weight = 280 lbf
We know that 1 lbf = 4.44 N
so 280 lbf = 1245.5 N
Weight =1245.5 N
Height h = 60 ft
We know that 
1 ft = 0.3048 m
So 60 ft = 18.28 m
  h =18.28 m
Power = 3.5 hp
We know that 
1 hp =0.74 KW
So 3.5 hp = 2.61 KW
Power = 2.61 KJ/s
So the work done by fireman = Weight x h
Now by putting the values
Work done by fireman= 1245.5 x 18.28 J
 Work done by fireman=   2267.74 J
Work done by fireman=   2.26774  KJ
We know that 1 Btu= 1.05 KJ
So   2.266 KJ = 2.15 Btu
Work done by fireman=   2.15  Btu
We know that ,rate of work is called power.
Power x time =  work
2.61 x t = 2.26
So t= 0.86 sec
 
        
             
        
        
        
<span>A transverse wave is a moving wave that consists of oscillations occurring perpendicular (or right angled) to the direction of energy transfer. If a transverse wave is moving in the positive x-direction, its oscillations are in up and down directions that lie in the y–z plane. Light is an example of a transverse wave.</span>
        
             
        
        
        
Answer:
Electromagnetic waves
Explanation:
Electromagnetic waves are waves that consist of oscillating electric and magnetic fields, that oscillate perpendicularly to each other and perpendicularly to the direction of propagation of the wave (for such a reason, these waves are also called transverse waves).
Electromagnetic waves always travel in a vacuum at the same speed, called speed of light:

and they are classified into 7 different types, according to their frequency. From lowest to highest frequency, we have:
Radio waves
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays
Therefore, gamma rays, x-rays, visible light and radio waves are all types of electromagnetic waves with different frequencies.