Answer:

Explanation:
given,
s = 400- 16 t²
we know,
Velocity of an object is defined as the change in displacement per unit change in time.
velocity an also be return as




Hence, instantaneous velocity function given by 
To calculate instantaneous velocity, you need to insert value of time.
ex, instantaneous velocity at t = 4 s
v = -32 x 4 = -128 m/s.
Answer:
The modern instruments or we can say the different levels of telescopes are used to explore and study the distant galaxies. i.e the Hubble telescope is out there providing the data regarding the different properties of the celestial entities which in other case is not visible to the human naked eye.
Explanation:
- Scientists and research workers are in constant search for more answers as they explore the universe and implement the laws of physics on the celestial entities. But, most of the objects inside the universe are not visible to human naked eye, as they are far from sight and thus more advanced form of instruments like the x-ray, optical, and light telescopes are used to determine the different properties of the celestial entities inside the universe.
- As, these telescopes includes the most recent "Hubble telescope", which is out there inside the space to explore the universe and more over the galaxies by subjecting them with x-rays and then provide us with a very rough but valid results to study the distant galaxies.
To solve this problem we will apply the concept related to destructive interference (from the principle of superposition). This concept is understood as a superposition of two or more waves of identical or similar frequency that, when interfering, create a new wave pattern of less intensity (amplitude) at a point called a node. Mathematically it can be described as

Where,
d = Path difference
= wavelength
n = Any integer which represent the number of repetition of the spectrum
In this question the distance between the two source will be minimum for the case of minimum path difference, then n= 1



Therefore the minimum distance that should you separate two sources emitting the same waves is 2.5mm
Answer:
a)
, b) 
Explanation:
a) Let consider two equations of equilibrium, the first parallel to ski slope and the second perpendicular to that. The equations are, respectively:
The force on the skier is:



b) The equations of equilibrium are the following:

The force on the skier is:



Answer:
Doppler effect, the apparent difference between the frequency at which sound or light waves leave a source and that at which they reach an observer, caused by relative motion of the observer and the wave source. This phenomenon is used in astronomical measurements, in Mössbauer effect studies, and in radar and modern navigation.
Explanation: