Homework Help Forum: physics 20

Posted by Adrienne on Tuesday, November 3, 2009 at 10:08pm.

A speed velocity of a a rocket with a mass of 0.25 kg passes from 15 m/s[up] to 40 m/s[up] in 0.60s. calculate the force of the escaped gasses of the rocket. **** that's what i've done, so far data: m = 0.25kg initial velocity = 15 m/s final velocity = 40 m/s time = 0.60s final velocity - initial velocity / time = acceleration 40 m/s - 15 m/s / 0.60 s = 41.67 m/s^2 for here the solutions for the problem says that the next formula that needs to be used is FORCE = MASS (GRAVITY + ACCELERATION) why is that. and why would you not use the formula force = mass x acceleration ?

• physics 20 - Jordan, Wednesday, November 4, 2009 at 7:58am

  acceleration due to gravity must be factored in as the rocket is traveling upwards. since you have chosen up to be positive acceleration down must be negative, making gravity -9.8m/s the equation is still force=mass x acceleration accept the formula used to calculate acceleration does not factor in gravity, the value calculated will just assume that no other forces are acting on the rocket i know this may not be the best clarification so ask away with any problems :)

  
  

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