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An interstellar ship has a mass of \(1.20 \times 10^{6} \mathrm{~kg}\) and is initially at rest relative to a star system. (a) What constant acceleration is needed to bring the ship up to a speed of \(0.10 c\) (where \(c\) is the speed of light, \(3.0 \times 10^{8} \mathrm{~m} / \mathrm{s}\) ) relative to the star system in \(3.0\) days? (b) What is that acceleration in \(g\) units? (c) What force is required for the acceleration? (d) If the engines are shut down when \(0.10 c\) is reached (the speed then remains constant), how long does the ship take (start to finish) to journey \(5.0\) light-months, the distance that light travels in \(5.0\) months?

Short Answer

Expert verified
The required acceleration is 115.7 m/s虏 (11.8 g), the force needed is 1.39 脳 10鈦 N, and the journey takes 5000 days.

Step by step solution

01

Determine Final Speed

The final speed of the ship is given as \(0.10c\), where \(c = 3.0 \times 10^8 \text{ m/s}\). Thus, the final speed \(v = 0.10 \times 3.0 \times 10^8 \text{ m/s} = 3.0 \times 10^7 \text{ m/s}\).
02

Calculate the Acceleration

We need to find the acceleration \(a\) needed to reach this speed in \(3.0\) days. First, convert time into seconds: \(3.0 \text{ days} = 3.0 \times 24 \times 3600 \text{ s} = 259200 \text{ s}\). Use the equation \(v = u + at\), where \( u = 0 \) (initial velocity). So, \(a = \frac{v}{t} = \frac{3.0 \times 10^7 \text{ m/s}}{259200 \text{ s}} \approx 115.7 \text{ m/s}^2\).
03

Convert Acceleration to g Units

The acceleration in units of \(g\) is \( a_g = \frac{a}{9.81} = \frac{115.7}{9.81} \approx 11.8 \text{ g}\).
04

Calculate the Required Force

The force \(F\) required can be found using Newton's second law, \(F = ma\). Here, \(m = 1.20 \times 10^{6} \text{ kg}\), so \(F = 1.20 \times 10^{6} \times 115.7 \approx 1.39 \times 10^8 \text{ N}\).
05

Calculating Journey Time for 5.0 Light-Months

First, convert 5.0 light-months to meters. One light-month is the distance light travels in a month: \(d_{light\text{-month}} = c \times \text{time in a month} = 3.0 \times 10^8 \times 30 \times 24 \times 3600\approx 2.592 \times 10^{15} \text{ m}\). Thus, \(5.0\) light-months \(= 5 \times 2.592 \times 10^{15} \approx 1.296 \times 10^{16} \text{ m}\). With speed \(v = 3.0 \times 10^7 \text{ m/s}\), the journey time is \( \text{Time} = \frac{d}{v} = \frac{1.296 \times 10^{16}}{3.0 \times 10^7} \approx 4.32 \times 10^8 \text{ s}\). Convert to days: \( \frac{4.32 \times 10^8}{3600 \times 24} \approx 5000 \text{ days}\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Relativistic Speed
In interstellar travel physics, reaching a significant fraction of the speed of light is often called travelling at relativistic speeds. When we say a ship accelerates to "0.10c," it means the ship is moving at 10% of the speed of light. The constant value for the speed of light is important: it is approximately \(3.0 \times 10^8\ \text{m/s}\). In our exercise, achieving 0.10c means reaching a speed of \(3.0 \times 10^7\ \text{m/s}\).
Understanding this concept is important because at these speeds, traditional physics slightly bends and the behavior of objects is dictated by Einstein鈥檚 theory of relativity. However, for the calculation purposes in this task, non-relativistic physics applies because 0.10c is considerably slower than near-light speeds where relativistic effects like time dilation or length contraction become pronounced.
  • Relativistic speeds are fractions of the speed of light.
  • In basic calculations, 0.10c often means simple multiplication with the constant \(c\).
  • Einstein鈥檚 relativity isn't profoundly necessary but is ideal in understanding potential effects.
Acceleration Calculation
Acceleration is the rate at which an object changes its velocity over time. In this scenario, we want to calculate the constant acceleration necessary for the ship to reach 0.10c from a rest position within 3 days. Time needs to be converted into seconds to match the velocity units.
Using the formula \(v = u + at\), where \(v\) is final velocity, \(u\) is initial velocity (0 in this case), \(a\) is acceleration, and \(t\) is time, we find that:
  • Final speed \(v = 3.0 \times 10^7\ \text{m/s}\)
  • Time \(t = 259200\ \text{s}\) (after converting from days)
  • Acceleration \(a = \frac{3.0 \times 10^7}{259200} \approx 115.7\ \text{m/s}^2\)
This straightforward calculation shows how to manipulate the equation to solve for different variables and derive acceleration using known values of speed and time.
Newton's Second Law
One of the fundamental principles in physics is Newton's Second Law of Motion, which states that force equals mass times acceleration (\(F = ma\)). In our scenario, to find the force needed for the desired acceleration, we combine known mass and the calculated acceleration.
The ship has a mass \(m\) of \(1.20 \times 10^6\ \text{kg}\) and an acceleration \(a\) of \(115.7\ \text{m/s}^2\). Therefore, the force required is:
  • \(F = 1.20 \times 10^6 \times 115.7\)
  • \(F \approx 1.39 \times 10^8\ \text{N}\)
This calculation is pivotal for understanding how much energy would be needed to drive the ship to that speed. Applying Newton's Second Law can help determine the necessary engine power for real-life space missions.
Distance and Time Conversion
Understanding how to convert distance and time is crucial in scenarios involving interstellar travel. The problem asks how long the ship takes to travel 5 light-months at 0.10c, necessitating a conversion of light-months to meters and travel time to days.
We determine that one light-month is the distance light travels in one month, approximately \(2.592 \times 10^{15}\ \text{m}\). For 5 light-months, the distance is \(1.296 \times 10^{16}\ \text{m}\). With a constant speed (after acceleration period) of \(3.0 \times 10^7 \text{m/s}\), the travel time becomes:
  • \( \text{Time} = \frac{d}{v} = \frac{1.296 \times 10^{16}}{3.0 \times 10^7} \approx 4.32 \times 10^8\ \text{s}\)
  • Converted to days: \( \approx 5000\ \text{days} \)
These conversions allow scientists to express travel distances and times in comprehensible units, providing essential data when planning interstellar missions.

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Most popular questions from this chapter

The only two forces acting on a body have magnitudes of \(20 \mathrm{~N}\) and \(35 \mathrm{~N}\) and directions that differ by \(80^{\circ}\). The resulting acceleration has a magnitude of \(20 \mathrm{~m} / \mathrm{s}^{2}\). What is the mass of the body?

An electron with a speed of \(1.2 \times 10^{7} \mathrm{~m} / \mathrm{s}\) moves horizontally into a region where a constant vertical force of \(4.5 \times\) \(10^{-16} \mathrm{~N}\) acts on it. The mass of the electron is \(9.11 \times 10^{-31} \mathrm{~kg}\). Determine the vertical distance the electron is deflected during the time it has moved \(30 \mathrm{~mm}\) horizontally.

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