Gravitational Force Physics Explanation

This problem involves three identical spheres interacting solely through gravity. They are initially placed at the vertices of an equilateral triangle and start moving towards each other due to gravitational attraction. We need to find how the collision time changes when both the initial separation distance and the masses of the spheres are altered.

Collision Time Proportionality

The time it takes for such a system to collapse under its own gravity can be shown to be proportional to the initial side length raised to the power of 3/2, and inversely proportional to the square root of the mass of the individual spheres. Mathematically, the collision time T follows the relation:

$T \propto \frac{a^{3/2}}{\sqrt{m}}$

Where:

• $T$ is the collision time.
• $a$ is the initial side length of the equilateral triangle.
• $m$ is the mass of each identical sphere.

Initial Collision Time Calculation

Let the initial collision time be $T_1$, initial side length be $a_1$, and initial mass be $m_1$. We are given:

• $T_1 = 4$ seconds
• $a_1 = a$
• $m_1 = m$

Using the proportionality:

$T_1 \propto \frac{a_1^{3/2}}{\sqrt{m_1}} \implies 4 \propto \frac{a^{3/2}}{\sqrt{m}}$

New Collision Time Calculation

Let the new collision time be $T_2$, new side length be $a_2$, and new mass be $m_2$. We are given:

• $a_2 = 2a$
• $m_2 = 2m$

Using the same proportionality for the new conditions:

$T_2 \propto \frac{a_2^{3/2}}{\sqrt{m_2}}$

Substitute the new values:

$T_2 \propto \frac{(2a)^{3/2}}{\sqrt{2m}}$

Simplify the expression:

$T_2 \propto \frac{2^{3/2} a^{3/2}}{\sqrt{2} \sqrt{m}} = \frac{2 \sqrt{2} a^{3/2}}{\sqrt{2} \sqrt{m}} = \frac{2 a^{3/2}}{\sqrt{m}}$

Collision Time Ratio

Now, we can find the ratio of the new collision time ($T_2$) to the initial collision time ($T_1$):

$\frac{T_2}{T_1} = \frac{2 a^{3/2}/\sqrt{m}}{a^{3/2}/\sqrt{m}}$

The terms $a^{3/2}/\sqrt{m}$ cancel out, leaving:

$\frac{T_2}{T_1} = 2$

Final Result Determination

We can now solve for $T_2$ using the initial time $T_1 = 4$ seconds:

$T_2 = 2 \times T_1 = 2 \times 4 \text{ seconds}$

$T_2 = 8 \text{ seconds}$

Therefore, if the sides of the triangle are increased to length 2a and the masses are made 2m, the spheres will collide after 8 seconds.