# Need help on question! newton's second law

1. Oct 14, 2008

### phynoob

1.Bsed on newton's 2nd law,predict what will happen to the spaceshutter's acceleration after a lift as it burns its fuel

2. Relevant equations F=ma

3. The attempt at a solution since fuel is being burnt, thus mass of space shutter is decreasing as fuel is being burnt. force is constant as it is determined by the gravitional force of earth on space shutter (correct me if im wrong,but constant i think). thus,acceleration will be increased in the space shutter.

thx for feedbacks!

2. Oct 14, 2008

### physics girl phd

You reasoning is good in that the acceleration is increased because the shuttle is losing mass. What isn't right is the stuff about your forces. Gravitational force is, in fact, technically not constant -- if your craft is going as high as low earth orbits like the international space station. It actually decreases (slightly... gravitational acceleration g goes from 9.8 to about 9.3 in that distance... graviational force decreases with distange). But in this case, the gravitational force isn't what causes the acceleration. What causes the acceleration is the "tossing away" of the molecules in the exhaust due to burning fuel... it's why you are losing weight in the craft. If you burn fuel at a constant rate, you'll have a more constant thrust force.

This simulation is fun and relates to the topic: http://phet.colorado.edu/simulations/sims.php?sim=Lunar_Lander

3. Oct 14, 2008

### phynoob

hmm..thx for the reply!
anyway,since my question didnt state anything about the forces,i think its ok for me not discuss about the forces.

but for learning sake, so the force that is acting on the space shutter is <9.8 and it is a constant?

am i right?

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