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inysia [295]
3 years ago
7

A paleontologist estimates that when a particular rock formed, it contained 12 mg of the radioactive isotope potassium-40, which

has a half-life of 1.26 billion years. The rock now contains 3 mg of the isotope. About how old is the rock? Enter in billions of years.
Physics
1 answer:
leva [86]3 years ago
7 0

Answer:

t = 2.52 billion \:years

Explanation:

As we know by radioactivity law

N = N_o e^{-\lambda t}

so here we will have

N = 3 mg

N_o = 12 mg

now we will have

3 = 12 e^{-\lambda t}

\lambda t = ln 4

now we also know that

\lambda = \frac{ln2}{1.26 \times 10^6 yrs}

t = 1.26\times 10^6\times \frac{ln4}{ln2}

t = 2.52 billion \:years

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A dolphin is able to tell in the dark that the ultrasound echoes received from two sharks come from two different objects only i
Vlad1618 [11]

Answer:

a) Wavelength of the ultrasound wave = 0.0143 m <<< 3.5m, hence its ability is not limited by the ultrasound's wavelength.

b) Minimum time difference between the oscillations = Period of oscillation = 0.00952 ms

Explanation:

The frequency of the ultrasound wave = 105 KHz = 105000 Hz. The speed of ultrasound waves in water ≈ 1500 m/s. Wavelength = ?

v = fλ

λ = v/f = 1500/105000 = 0.0143 m <<< 3.5m

This value, 0.0143m is way less than the 3.5m presented in the question, hence, this ability is not limited by the ultrasound's wavelength.

b) Minimum time difference between the oscillations = The period of oscillation = 1/f = 1/105000 = 0.00000952s = 0.00952 ms

Hope this helps!

6 0
3 years ago
What is the mirror formula for curved mirrors
Reika [66]
The mirror formula for curved mirrors is:
\frac{1}{f}= \frac{1}{d_o}+ \frac{1}{d_i}
where
f is the focal length of the mirror
d_o is the distance of the object from the mirror
d_i is the distance of the image from the mirror

The sign convention that should be used in order to find the correct values is the following:
- f: positive if the mirror is concave, negative if the mirror is convex
- d_i: positive if the image is real (located on the same side of the object), negative if it is virtual (located on the opposite side of the mirror)

3 0
3 years ago
Read 2 more answers
A weight lifter applies an upward force of 1100 N while lowering a dumbbell
Paul [167]

Answer:

A

Explanation:

work = force \times distance

work = 1100 \times 0.5

= 550 \: j

hope it helped a lot

pls mark brainliest with due respect .

6 0
3 years ago
Can waves move or transport matter? Why or why not?
OLga [1]
They can.
Surfers use waves to move themselves around.
6 0
3 years ago
A stone is dropped into a well. The sound of the splash is heard 3.5 seconds later. What is the depth of the well? Take the spee
Naddika [18.5K]

Answer:

The depth of the well, s = 54.66 m

Given:

time, t = 3.5 s

speed of sound in air, v = 343 m/s

Solution:

By using second equation of motion for the distance traveled by the stone when dropped into a well:

s = ut +\frac{1}{2}at^{2}

Since, the stone is dropped, its initial velocity, u = 0 m/s

and acceleration is due to gravity only, the above eqn can be written as:

s = \frac{1}{2}gt'^{2}

s = \frac{1}{2}9.8t^{2} = 4.9t'^{2}                     (1)

Now, when the sound inside the well travels back, the distance covered,s is given by:

s = v\times t''

s = 343\times t''                                              (2)

Now, total time taken by the sound to travel:

t = t' + t''

t'' = 3.5 - t'                                                                        (3)

Using eqn (2) and (3):

s = 343(3.5 - t')                                                                 (4)

from eqn (1) and (4):

4.9t'^{2} = 343(3.5 - t')

4.9t'^{2} + 343t' - 1200.5 = 0

Solving the above quadratic eqn:

t' = 3.34 s

Now, substituting t' = 3.34 s in eqn (2)

s = 54.66 m

3 0
3 years ago
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