Complete Question 
A commuter train passes a passenger platform at a constant speed of 39.6 m/s. The train horn is sounded at its characteristic frequency of 350 Hz. 
(a)
 What overall change in frequency is detected by a person on the platform as the train moves from approaching to receding
(b) What wavelength is detected by a person on the platform as the train approaches?
  
Answer:
a
   
b
   
Explanation:
From the question we are told that 
       The speed of the train is  
       The frequency of the train horn is  
Generally the speed of sound has a constant values of  
   Now  according to dopplers equation when the train(source) approaches a person on the platform(observe) then the frequency on the sound observed by the observer can be mathematically represented as  
         
substituting values 
         
        
   Now  according to dopplers equation when the train(source) moves away from  the  person on the platform(observe) then the frequency on the sound observed by the observer can be mathematically represented as  
            
substituting values 
         
        
The overall change in frequency is detected by a person on the platform as the train moves from approaching to receding is mathematically evaluated as 
         
         
         
Generally the wavelength detected by the person as the train approaches  is mathematically represented  as 
           
           
          
 
        
             
        
        
        
48 M to get the answer add the area of the triangle and rectangle under the line
        
             
        
        
        
Answer:
A : the colonists dumped tea in Boston Harbor
 
        
             
        
        
        
You said                        T           =  mg + ma
Subtract  mg  
from each side:            T - mg  =            ma
Divide each side by  m :      a  =  (T-mg) / m
                                          or  a  =  T/m  -  g
        
             
        
        
        
Explanation:
Let the distance covered by the body be s, initial and final velocities be u and v respectively and time taken be t. 
 
 
By first equation of motion: 
 
 
Substituting the value of v in equation (1), we find:
 
 
Hence proved.