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NATURE.M
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So suppose an astronaut in interstellar space has gas ejecting from her propulsion system.
So the gas would cause her to move forward by some distance, d. Then, the F[itex]_{thrust}[/itex] acting on her must be constant (assuming the amount of gas ejected per unit time is constant, and the speed it is released at is constant). Then, since the mass of the system (astronaut+equipment) is decreasing the acceleration of the system must be increasing to enable the F[itex]_{thrust}[/itex] to remain constant. Please correct me if my reasoning is wrong.
(1) So naturally it wouldn't be valid to calculate the distance she travels by finding the acceleration from Newtons second law, and using that along with a kinematical equation to solve for the distance d (since the acceleration isn't constant).
(2) So instead I would use [itex]v = v_{g}ln \frac{m_{i}}{m_{f}}[/itex], where [itex]v_{g}[/itex] is the speed of the gas being ejected.
Then integrate for the position , [itex] x(t) = \int_o^t {v_{g}ln \frac{m_{i}}{m_{f}}}dt[/itex],
where [itex]m_{f}=m_{i} - \frac{dm}{dt}t[/itex], where [itex]\frac{dm}{dt}[/itex] is the rate at which gas is ejected.
But then for a question I had to do, both methods (1 and 2) produced the same final answer which I found to be very odd. Any possible explanations?
So the gas would cause her to move forward by some distance, d. Then, the F[itex]_{thrust}[/itex] acting on her must be constant (assuming the amount of gas ejected per unit time is constant, and the speed it is released at is constant). Then, since the mass of the system (astronaut+equipment) is decreasing the acceleration of the system must be increasing to enable the F[itex]_{thrust}[/itex] to remain constant. Please correct me if my reasoning is wrong.
(1) So naturally it wouldn't be valid to calculate the distance she travels by finding the acceleration from Newtons second law, and using that along with a kinematical equation to solve for the distance d (since the acceleration isn't constant).
(2) So instead I would use [itex]v = v_{g}ln \frac{m_{i}}{m_{f}}[/itex], where [itex]v_{g}[/itex] is the speed of the gas being ejected.
Then integrate for the position , [itex] x(t) = \int_o^t {v_{g}ln \frac{m_{i}}{m_{f}}}dt[/itex],
where [itex]m_{f}=m_{i} - \frac{dm}{dt}t[/itex], where [itex]\frac{dm}{dt}[/itex] is the rate at which gas is ejected.
But then for a question I had to do, both methods (1 and 2) produced the same final answer which I found to be very odd. Any possible explanations?