How is the world population projected to change in the next few decades?

The cheetahs in Kenya and the cheetahs in Tanzania make up separate _____.

Andreyy89

C. Populations.
Hope that's right.

6 0

3 years ago

NASA is giving serious consideration to the concept of solar sailing. A solar sailcraft uses a large, low- mass sail and the ene

RUDIKE [14]

Answer:

d. The sail should be reflective because in this case the momentum transferred to the sail per unit area per unit time is larger than for absorbing sail, therefore the radiation pressure is larger for the reflective sail.

Explanation:

Let us take the momentum of a photon unit as u

we know that the rate of change of momentum is proportional to the force exerted.

For a absorbing surface, the photon is absorbed, therefore the final momentum is zero. From this we can say that

F = (u - 0)/t = u/t

for a unit time, the force is proportional to the momentum of the wave due to its energy density. Therefore,

F = u

For a reflecting surface, the momentum of the wave strikes the sail and changes direction. Since we know that the speed of light does not change, then the force is proportional to

F = (u - (-u))/t = 2u/t

just as the we did above, it becomes

F = 2u.

From this we can see that the force for a reflective sail is twice of that for an absorbing sail, and we know that the pressure is proportional to the force for a given area. From these, we conclude that the sail should be reflective because in this case the momentum transferred to the sail per unit area per unit time is larger than for absorbing sail, therefore the radiation pressure is larger for the reflective sail.

3 0

3 years ago

The height of the empire state building is 318 m if a stone is dropped from the top of the building what is the stones velocity

lutik1710 [3]

79 m/s. A stone dropped from the top of the Empire State Building will have a velocity of 79 m/s just before it strikes the ground.

This problem is about free fall, to find the velocity of the stone before it strikes the ground we have to use the equation $v_{f}^{2}=v_{0}^{2}+2gh$ , the initial velocity of the stone is 0 m/s. Then: