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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, \(\left.3.0 \times 10^{8} \mathrm{~m} / \mathrm{s}\right)\) 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
Acceleration: \(a = 11.57 \ \text{m/s}^2\). Acceleration in \(g\): 1.18. Force: \(F = 13.89 \times 10^6 \ \text{N}\). Total journey: 50 months.

Step by step solution

01

Understand the problem's requirements

This problem involves calculating the acceleration, force, and travel time for a spacecraft reaching a specified speed and covering a specific distance. You're given the mass of the ship, initial and final velocity, desired time to reach the speed, and total travel distance. You'll also convert units where necessary.
02

Calculate required acceleration

First, calculate the ship's acceleration to reach a speed of \(0.10c\) in 3.0 days. Use the formula for acceleration \( a = \frac{\Delta v}{\Delta t} \). Substitute \( \Delta v = 0.10 \times 3.0 \times 10^8 \ \text{m/s} \) and \( t = 3.0 \times 24 \times 3600 \ \text{s} \). Simplify to find \( a \).
03

Convert acceleration to 'g' units

Convert the previously calculated acceleration to units of \( g \), where \( 1g = 9.81 \ \text{m/s}^2 \). Use the formula \( a_{g} = \frac{a}{9.81} \) to find the acceleration in \( g \) units.
04

Calculate the required force

Calculate the force needed to achieve the calculated acceleration using the formula \( F = ma \). Substitute the mass of the ship \( m = 1.20 \times 10^6 \ \text{kg} \) and the acceleration \( a \) from the first calculation to find the force \( F \).
05

Determine travel time for 5.0 light-months

Determine how long the journey takes over the 5.0 light-months with the ship traveling at a constant speed of \(0.10c\). First, find the distance in meters corresponding to 5.0 light-months: \( 5.0 \times 2.998 \times 10^8 \times 30 \times 24 \times 3600 \). Then calculate the time using \( t = \frac{d}{v} \), where \( v = 0.10 \times 3.0 \times 10^8 \ \text{m/s} \).

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Key Concepts

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

Acceleration Calculation
To find the acceleration needed for the spacecraft, we use the formula for acceleration: \( a = \frac{\Delta v}{\Delta t} \). Let's break that down:- \( \Delta v \) represents the change in velocity, which is from rest (0) to \( 0.10c \), where \( c \) is the speed of light, or \( 3.0 \times 10^8 \text{ m/s} \). Hence, \( \Delta v = 0.10 \times 3.0 \times 10^8 \text{ m/s} \).- We need to convert the given time of 3 days into seconds to align with the SI unit system. So, \( 3 \text{ days} \times 24 \text{ hours/day} \times 3600 \text{ seconds/hour} = 259,200 \text{ seconds} \).Plug these values into the acceleration formula to get:\[a = \frac{0.10 \times 3.0 \times 10^8}{259,200} \approx 1156 \text{ m/s}^2\]This is the constant acceleration required for the spacecraft to reach 0.10 times the speed of light in 3.0 days.
Conversion to g Units
In physics, comparing acceleration with Earth's gravity, \( g \), is common because it provides an intuitive grasp of the scale of acceleration. Earth’s gravitational acceleration, \( g \), is approximately \( 9.81 \text{ m/s}^2 \).
To convert the calculated acceleration to \( g \) units, use the formula:\[a_{g} = \frac{a}{9.81}\]- Substitute the value of \( a \) from the previous calculation: \( a = 1156 \text{ m/s}^2 \).
- So, \( a_g = \frac{1156}{9.81} \approx 117.87g \).Therefore, the constant acceleration required is about \( 117.87 \g \) when expressed in Earth gravity units.
Force Equation
To calculate the force required to achieve this acceleration, we apply Newton's second law of motion:
\( F = ma \), where \( F \) is the force, \( m \) is the mass, and \( a \) is the acceleration.
- Here, \( m = 1.20 \times 10^6 \text{ kg} \) (the mass of the spacecraft).- And \( a = 1156 \text{ m/s}^2 \).Substituting these values into the formula:\[F = 1.20 \times 10^6 \times 1156 \approx 1.39 \times 10^9 \text{ N}\]This calculation shows that a force of approximately \( 1.39 \times 10^9 \) newtons is needed to propel the spacecraft to the desired speed within the given timeframe.
Light-Month Distance Calculation
Understanding the concept of a light-month can provide insight into the vastness of space distances. 1 light-month is the distance that light travels in one month.- Light speed, \( c = 3.0 \times 10^8 \text{ m/s} \).- Number of seconds in a month: \( 30 \times 24 \times 3600 \text{ s} \).To find the distance light travels in 5 months:\[\text{Distance} = 5 \times c \times \text{seconds in a month}\]Plug in the values:\[\text{Distance} = 5 \times 3.0 \times 10^8 \times 30 \times 24 \times 3600 \approx 3.89 \times 10^{15} \text{ m}\]The next step is calculating the travel time for this distance at a constant speed of \( 0.10c \).- The speed of the ship, \( v = 0.10 \times 3.0 \times 10^8 \text{ m/s} \).To find the time \( t \), use: \( t = \frac{d}{v} \)\[t = \frac{3.89 \times 10^{15}}{0.10 \times 3.0 \times 10^8} \approx 1.30 \times 10^7 \text{ s}\]Converting seconds to different units, such as hours or days, can be done for practical purposes, knowing there are 3600 seconds in an hour.

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Most popular questions from this chapter

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