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slava [35]
3 years ago
13

The rubidium isotope 87Rb is a β emitter that has a half-life of 4.9 ✕ 1010 y that decays into 87Sr. It is used to determine the

age of rocks and fossils. Rocks containing the fossils of early animal have a ratio of 87Sr to 87Rb of 0.0040. Assuming that there was no 87Sr present when the rocks were formed, calculate the age of the fossils.
Physics
1 answer:
fredd [130]3 years ago
4 0

Answer:

t = 39.04 1010 year

Explanation:

This is a nuclear disintegration exercise that is governed by the equation.

     N = N0 e (-lam t)

The average life time is related to nuclear activity

      T ½ = ln 2 / lam

Let's use these two equations for exercise, let's start by finding nuclear activity

     Lam = ln 2 / T ½

     Lam = ln 2 / 4.9 10 10

    Lam = 0.14146 10-10 y-1

They tell us that the relationship atoms

      No / N = 0.0040

Let's look

       No / N = 1/0040

       N/No = 250                                                                                                                                                                                

Let's calculate the time

       (-lam t) = ln (N / No)

,        t = - 1 / lam ln (n / No)

        t = - 1 / 0.14146 10-10 ln (250)

        t = 39.04 1010 year

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A 5 kg block is sliding down a plane inclined at 30^0 with a constant velocity of 4 m/s. To determine the coefficient of frictio
Leya [2.2K]

Answer:

The necessary information is if the forces acting on the block are in equilibrium

The coefficient of friction is 0.577

Explanation:

Where the forces acting on the object are in equilibrium, we have;

At constant velocity, the net force acting on the particle = 0

However, the frictional force is then given as

F = mg sinθ

Where:

m = Mass of the block

g = Acceleration due to gravity and

θ = Angle of inclination of the slope

F = 5×9.81×sin 30 = 24.525 N

Therefore, the coefficient of friction is given as

24.525 N = μ×m×g × cos θ = μ × 5 × 9.81 × cos 30 = μ × 42.479

μ × 42.479 N= 24.525 N

∴ μ = 24.525 N ÷ 42.479 N = 0.577

3 0
3 years ago
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5,6,1,9,21,37,68 ? find missing​
maria [59]

Answer:

Missing numbers are 3,11,13, 15,17,19, 23,27,29 and wrong are 6,68

4 0
3 years ago
The earplug can reduce the sound level to about 18 decibels (dB). What percentage reduction is this intensity?
zlopas [31]

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1 x 10 -10 whisper at 1m distance.

Explanation:

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A solid cylinder has a mass of 5 kg and radius of 2 m and is fixed so that it is able to rotate freely around its center without
kari74 [83]

Answer:

0.893 rad/s in the clockwise direction

Explanation:

From the law of conservation of angular momentum,

angular momentum before impact = angular momentum after impact

L₁ = L₂

L₁ = angular momentum of bullet = + 9 kgm²/s (it is positive since the bullet tends to rotate in a clockwise direction from left to right)

L₂ = angular momentum of cylinder and angular momentum of bullet after collision.

L₂ = (I₁ + I₂)ω where I₁ = rotational inertia of cylinder = 1/2MR² where M = mass of cylinder = 5 kg and R = radius of cylinder = 2 m, I₂ = rotational inertia of bullet about axis of cylinder after collision = mR² where m = mass of bullet = 0.02 kg and R = radius of cylinder = 2m and ω = angular velocity of system after collision

So,

L₁ = L₂

L₁ = (I₁ + I₂)ω

ω = L₁/(I₁ + I₂)

ω = L₁/(1/2MR² + mR²)

ω = L₁/(1/2M + m)R²

substituting the values of the variables into the equation, we have

ω = L₁/(1/2M + m)R²

ω = + 9 kgm²/s/(1/2 × 5 kg + 0.02 kg)(2 m)²

ω = + 9 kgm²/s/(2.5 kg + 0.02 kg)(4 m²)

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ω = +9 kgm²/s/10.08 kgm²

ω = + 0.893 rad/s

The angular velocity of the cylinder bullet system is 0.893 rad/s in the clockwise direction-since it is positive.

7 0
3 years ago
An object is allowed to fall freely near the surface of an unknown planet. The object falls 72 meters from rest in 4.0 seconds.
dimaraw [331]
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7 0
3 years ago
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