Wave speed = frequency * wavelength
Input the numbers into this equation :
Wave speed = 200 * 3
Work it out and you will get the answer :
Wave speed = 600 m/s
Efficiency = (useful output) / (input)
Efficiency = (35 J) / (125 J) = 0.28 = 28%
Answer:
(a) Time t = 16.46 sec
(b) Time t =13.466 sec
(c) Deceleration = 
Explanation:
(a) As the train starts from rest its initial velocity u = 0 m/sec
Acceleration 
Final speed v = 80 km/hr

From first equation of motion v =u+at
So 
(b) Now initial speed u = 22.22 m/sec
As finally train comes to rest so final speed v=0 m/sec
Deceleration 
So 
(c) We have given that initial velocity = 80 km/hr = 22.22 m/sec
Final velocity v = 0 m/sec
Time t = 8.30 sec
So acceleration is given by

As acceleration is negative so it is a deceleration
The correct answer (sample response) is:
The image seems to be behind the mirror, but nothing is really there.
Include the following in your response:
The image appears to be behind the mirror.
If someone looks behind the mirror, there is no image there.

The only answer that can justify being a hypothesis is C.