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Thread: Net force on astronaut

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    Student Karldahemster's Avatar
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    Net force on astronaut

    A rocket of mass 2000 tonnes, produces a constant thrust of 8x10^7N during liftoff by expelling 1500kg of exhaust gas per second.

    Calculate the net force acting on an 85kg astronaut 30s after liftoff.
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    Senior Member jazz519's Avatar
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    Re: Net force on astronaut

    a=T-mg/m

    so T is constant = 8x10^7
    m=(Initial mass of the rocket + fuel system) - (mass of fuel ejected)
    = 2000x1000-1500x30
    = 1955000 kg

    so a=T-mg/m
    = 8x10^7-1955000(9.8)/1955000
    = 39.9207161125 m/s^2

    F=ma
    = 1955000(39.9207161125)
    = 3393.26086957 N
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    Student Karldahemster's Avatar
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    Re: Net force on astronaut

    Quote Originally Posted by jazz519 View Post
    a=T-mg/m

    so T is constant = 8x10^7
    m=(Initial mass of the rocket + fuel system) - (mass of fuel ejected)
    = 2000x1000-1500x30
    = 1955000 kg

    so a=T-mg/m
    = 8x10^7-1955000(9.8)/1955000
    = 39.9207161125 m/s^2

    F=ma
    = 1955000(39.9207161125)
    = 3393.26086957 N
    Thanks, that's what I thought however, the solution just used a=F/m so must have been incorrect.
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    Senior Member jazz519's Avatar
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    Re: Net force on astronaut

    f=ma sorry on the last bit should be 85 instead of 1955000 (used it for the end answer but forgot to change it in the typed one)
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