Use the concept of beat frequency to find the applicable final freqeuncy for 20Hz beat frequency.
Beat can be defined as 'the interference pattern between two sounds of slightly different frequencies0
The expression for beat frequency is given as
Where,
Final frequency
Initial frequency
The beat frequency for us is 25Hz and the initial frequency is 240Hz, then
Being an absolute value, two values are possible, both in addition and subtraction:
The two possible values are
Answer:
300 m
Explanation:
The train accelerate from the rest so u = 0 m/sec
Final speed that is v = 80 m/sec
Time t = 30 sec
The distance traveled by first plane = 1200 m
We know the equation of motion 
where s is distance a is acceleration and u is initial velocity
Using this equation for first plane 
As the acceleration is same for both the plane so a for second plane will be 2.67 
The another equation of motion is 
using this equation for second plane 
s = 300 m
There are NO true statements on that list of choices.
Answer:
opposite charges attract each other while same charges repel each other.
~batmans wife dun dun dun.....
