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3 years ago

A sample of a radioactive substance is reduced to 1.0 gram after 4 half-lives. Determine the mass of the original sample

Physics

1 answer:

luda_lava [24]3 years ago

6 0

After 4 half-lives, there was 1 gram.

1 half-life earlier, after 3 half-lives, there must have been 2 grams.

1 half-life earlier, after 2 half-lives, there must have been 4 grams.

1 half-life earlier, after 1 half-life, there must have been 8 grams.

1 half-life earlier, when it started decaying, there must have been 16 grams. (B)

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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

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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.

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3 years ago

How does the theory of plate tectonics support the theory of seafood spreading?

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3 years ago

A jet travels 2250 km westward at a speed of 960 km/hr. it then encounters a strong headwind and its speed drops to 805 km/hr fo

Kipish [7]

For the first part of the trip:
we have velocity = 960 km/hr and distance = 2250 km
velocity = distance / time
time1 = distance / velocity = 2250 / 960 = 2.34375 hours

For the second part of the trip:
we have velocity = 805 km/hr and distance = 1320 km
velocity = distance / time
time2 = distance / velocity = 1320 / 805 = 1.63975 hours

For the total trip:
we have:
total distance covered = 2250 + 1320 = 3570 km
total time taken = 2.34375 + 1.63975 = 3.9835 hours
average velocity = total distance / total time
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3 years ago