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podryga [215]
3 years ago
15

"In a bad late-night science fiction film, a villain is using a large collection of radioactive atoms as energy for a weapon to

threaten the good guys. The atoms have a half-life of 1 hour. The villain has 4 kilograms of the radioactive material now, and he needs a minimum of 1 kg. for his weapon to work. After how much time will the weapon no longer be a threat?"
Physics
1 answer:
Veronika [31]3 years ago
3 0

Answer:

t=1.4hours

Explanation:

The half life is 1hour

At t=0 he has a mass of 4kg

So he want it to be 1kg, so that his weapon can work.

Applying the exponential function of decay

M=Cexp(-kt)

Where,

M is the mass at any time

C is a constant of integration

k is the rate of decay

Given that it has an half life of 1 hours.

Then k is 1

At t =0 the mass is 4kg

Therefore

4=Cexp(0)

C=4

M=4exp(-kt)

Since rate of decay is 1, then k=1

M=4exp(-t)

We need to find t at M=1kg

1=4exp(-t)

1=4exp(-t)

1/4=exp(-t)

0.25=exp(-t)

Take In of both sides

In(0.25)=-t

-1.3863=-t

Then, t=1.386hour

Then it will take about 1.4 hours to get to 1kg.

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Answer:

96%

Explanation

Let A the total area of the galaxy, is modeled as a disc:

A = πR^2 = π (25 kpc)^2

And let a be the area that astronomers are able to see:

a = πr^2 = π(5 kpc)^2

The percentage that can be seen is equal to 100 times the ratio of the areas, of the galaxy and the "visible" part:

P = 100 a/A = (5/25)^2 = 100/25 = 4%

Therefore, the percentage of the galaxy not included, i.e. not seen is:

(100-4)% = 96%

5 0
3 years ago
A car is moving north on a freeway. If a bug is flying south on the freeway, is the momentum of the bug positive or negative?
faltersainse [42]

Negative

Because the car is moving up and the bug is moving down. but it also depends on the weather so choice between one of those two I think is Negative but I may be wrong.

3 0
2 years ago
True or False
Ann [662]
The is true because I said so
7 0
2 years ago
Read 2 more answers
Spiderman, whose mass is 70.0 kg, is dangling on the free end of a 12.2-m-long rope, the other end of which is fixed to a tree l
Lana71 [14]

Answer:

U = -3978.8 J

Explanation:

The work of the gravitational force U just depends of the heigth and is calculated as:

U = -mgh

Where m is the mass, g is the gravitational acceleration and h the alture.

for calculate the alture we will use the following equation:

h = L-Lcos(θ)

Where L is the large of the rope and θ is the angle.

Replacing data:

h = 12.2-12.2cos(58.4)

h = 5.8 m

Finally U is equal to:

U = -70(9.8)(5.8)

U = -3,978.8 J

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3 years ago
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slavikrds [6]

Answer:

Recessed incandescent luminaires not marked type ic and those marked for installing directly in insulated ceilings must not have insulation over the top of the luminaire.

Explanation:

Depending on how they interact with insulation, lighting fixtures are rated at various levels. Non-IC rated lighting fixtures can accommodate higher wattage bulbs, but they also pose the greatest fire risk when used with the incorrect insulation.

In locations with insulation, light fixtures that are not IC rated may be installed. But there is a condition. The distance between the fixture and any insulation should be 3 inches. But the 3 inch gap in the insulation would negate the goal of insulation by producing a lot of uninsulated space, so this defies logic. Building a box-style cover to cover the fixture on the attic side is one option to fix this. Drywall or foil-faced foam insulation can be used to create this box. After the cover is put in place, insulation can be added for maximum effectiveness.

To learn more about recessed incandescent luminaries. Click brainly.com/question/17218799

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2 years ago
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