1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Newton's 3rd law help

  1. Feb 6, 2008 #1
    Could someone please check my work and verify if I am correct? I am not confident about any of my answers except #1. Thank you very much for your time.

    1. The initial mass of a giant rocket is 25000kg. What is the weight of the rocket?
    Answer: 250,000 N

    2. Assume 90% of the mass of the rocket is fuel and is spewed out nearly instantaneously. If the fuel for the rocket travels downward at a velocity of 50 m/s after being accelerated for 2 seconds then what is the force on the rocket's fuel? Ignore gravity on this one.
    Answer: A=change in velocity/T so a=25 m/s^2. Then I did F=MA so F=22,500kg*25m/s = 562,500 Is this correct?

    3. A.What is the net force on the rocket (remember gravity)?
    Answer: F=MA so 2500kg*10m/s= 25,000N I am really iffy about this one

    B. What is the acceleration of the rocket?
    Answer: A=f/m so a=25,000N/2500kg= 10m/s^2 ????????

    C. After 2 seconds how fast will the rocket be traveling?
    Answer: V=at so V=10m/s^2 * 2s= 20m/s ???

    4. Somehow we get the rocket into orbit around the earth.
    A. What is the weight of the rocket in orbit (mass = 2500 kg now)?
    Answer: F=MA so F=2500kg*10m/s= 25,000N. I wasn't sure what the acceleration would be for this one.

    B. If an astronaut applies a force of 750N to the rocket then what will the acceleration of the rocket be?
    Answer: A=F/M so A=25,750N??/2500 kg = 10.3 m/s^2 ?????

    C. The astronaut forgot to tether himself! What will the acceleration of the astronaut be (mass of astronaut is 100N)?
    Answer: A=F/M so A= 750N/100N= 7.5 m/s^2

    Again thanks for your time. I really need some help with this
     
  2. jcsd
  3. Feb 6, 2008 #2
    All correct.
     
  4. Feb 6, 2008 #3
    Thanks for the quick response.

    Anyone else care to verify that I am correct?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Newton's 3rd law help
  1. Help newton's 3rd law (Replies: 1)

Loading...