Answer:
The force is pull or push acting on the body which tends to change its state of rest or of motion is called force.
There are two types of force:
1.Contact force
2. Non-Contact
Answer:
The value is
Explanation:
From the question we are told that
The length of the crack is
The frequency is
The distance outside the cave that is being consider is
The speed of sound is 
Generally the wavelength of the wave is mathematically represented as

=> 
=> 
Generally for a single slit the path difference between the interference patterns of the sound wave and the center is mathematically represented as

=> 
=> 
Generally the width of the sound beam is mathematically represented as

=> 
=>
To solve the exercise it is necessary to take into account the definition of speed as a function of distance and time, and the speed of air in the sound, as well

Where,
V= Velocity
d= distance
t = time
Re-arrange the equation to find the distance we have,
d=vt
Replacing with our values


It is understood that the sound comes and goes across the entire lake therefore, the length of the lake is half the distance found, that is



Therefore the length of the lake is 634,55m
C. This is the idea of "black body radiation". Charcoal/carbon is a "perfect black body". Absorbs all radiation. There's a whole host of stuff about this in physics, including, I think, Planck's (Nobel Prize winner) black body radiation theory.
Karma, and sensei. Maybe nagisa