**Answer:**

ans: 1.26 × 10^(-6) N

**Explanation:**

suppose that;

mass of Justhin ( m) = 74 kg

mass of Christian (M) = 64 kg

distance of separation (d) = 0.5 m

universal gravitational constant(G) =6.67 × 10^(-11) Nm²/kg²

so,

gravitational force between them(F) = GmM/d²

F = (6.67 × 74× 64)/ ( 10¹¹× 0.5²)

= (1.26 × 10⁵)/ 10¹¹

= 1.26 × 10^(-6) N

**Answer:**

High amplitude is equivalent to loud sounds.

**Explanation:**

**Answer:**

T₂ = 18.65 °C (For Steel)

The temperature of steel first becomes 12 MPa at a temperature of 18.65°C

**Explanation:**

The formula for stress due to temperature difference in a member is given as follows:

**Stress = αEΔT**

where,

Stress = 12 MPa = 12 x 10⁶ Pa

α = co-efficient of linear expansion of the material

E = Young's Modulus of the Material

ΔT = Temperature Difference = Final Temperature - Initial Temperature

**12 x 10⁶ Pa = αE(T₂ - 15°C)**

<u>**FOR MAGNESIUM:**</u>

α = 25.2 x 10⁻⁶ /°C

E = 45 x 10⁹ Pa

Therefore,

**12 x 10⁶ Pa = (25.2 x 10⁻⁶/°C)(45 x 10⁹ Pa)(T₂ - 15°C)**

**T₂ - 15°C = (12 x 10⁶ Pa)/(1.134 x 10⁶ Pa/°C)**

**T₂ = 15°C + 10.58°C**

**T₂ = 25.58 °C (For Magnesium)**

<u>**FOR STEEL:**</u>

α = 17.3 x 10⁻⁶ /°C

E = 190 x 10⁹ Pa

Therefore,

**12 x 10⁶ Pa = (17.3 x 10⁻⁶/°C)(190 x 10⁹ Pa)(T₂ - 15°C)**

**T₂ - 15°C = (12 x 10⁶ Pa)/(3.287 x 10⁶ Pa/°C)**

**T₂ = 15°C + 3.65°C**

<u>**T₂ = 18.65 °C (For Steel)**</u>

<u>**The temperature of steel first becomes 12 MPa at a temperature of 18.65°C**</u>

**Answer:**

3.7 m/s^2

**Explanation:**

The period of a pendulum is given by:

where L is the length of the pendulum and g is the free-fall acceleration on the planet.

In this problem, we know that the period of the pendulum on Earth is:

while the period of the same pendulum on Mars is

And since the length of the pendulum L does not change, we can write:

where

is the free-fall acceleration on Earth

is the free-fall acceleration on Mars

Re-arranging the equation and substituting numbers, we find:

The **age** of the **universe** can be calculated by : dark energy, the age of the oldest stars patterns of background **radiation**, and the **speed **of **distant galaxies** moving away from the Earth.

Anything that acts as a container for **energy** and matter is known as the **universe**. The modern definition of** **the** universe** is the place that has time itself including the other heavenly entities like** Comets**, meteors, Stars, Planets, and many more.

The age of the **universe** is determined by scientists using the following ways:

- Concept of
**dark energy** is the property of space and it is used to predict the age of the universe as this form of energy is observed to expand the universe rapidly. - The age of the oldest star patterns of
**background radiation** is another way to determine the age of the **universe** as the first generation of stars are formed after the big bang. - As per the Hubble's relation, the galaxies move away from the
**Earth** at a certain **speed** are proportional to their distance. In other words, galaxies are farther as they are moving away from the **Earth**.

Thus, we can conclude that the age of the **universe** can be calculated by dark energy, the age of the oldest stars patterns of background radiation, and the speed of **distant galaxies** moving away from the** Earth**.

Learn more about the universe here:

brainly.com/question/9724831