physics 20

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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.
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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 -

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 :)