Answer:
a

b

Explanation:
From the question we are told that
The speed of the spaceship is 
Here c is the speed of light with value 
The length is 
The distance of the star for earth is 
The speed is 
Generally the from the length contraction equation we have that
![l = l_o \sqrt{1 -[\frac{v}{c } ]}](https://tex.z-dn.net/?f=l%20%20%3D%20%20l_o%20%20%5Csqrt%7B1%20-%5B%5Cfrac%7Bv%7D%7Bc%20%7D%20%5D%7D)
Now the when at rest the length is 
So



Considering b
Applying above equation
![l =l_o \sqrt{1 - [\frac{v}{c } ]}](https://tex.z-dn.net/?f=l%20%20%3Dl_o%20%5Csqrt%7B1%20-%20%20%5B%5Cfrac%7Bv%7D%7Bc%20%7D%20%5D%7D)
Here 
So



Answer:
The correct option is (c).
Explanation:
Given that,
The energy of a photon is, 
We need to tell the color of this light. We know that, the energy of a photon is given by :

Where
c is the speed of light

The wavelength of yellow light is approx 580 nm. Hence, we can say that this photon corresponds to yellow light.
Answer:

Explanation:
From the question we are told that:
Frictional force 
Coefficient of kinetic friction 
Generally the equation for Normal for is mathematically given by

Therefore


Air caught in the ball of foil makes the ball less dense than water
Answer:
we can say that wind energy is due to
D) Severe thunderstorms
Explanation:
As we know that wind energy is converted into kinetic energy of wind mills
This kinetic energy of wind mill is then converted into electrical energy using turbine
now we can consider here energy conservation theory that energy is only converted from one form to other form
it neither be destroyed nor be created but it can transfer from one form to other form
So here we can say that wind energy is due to
D) Severe thunderstorms