2011hope Posted June 14, 2009 Report Share Posted June 14, 2009 In the examkrackers mini mcat book exam 2 physics section I find that in the answer for question 55 we assume that the vertical acceleration for the projectiles is g (10 m/s^2). But then in question 60 we assume the vertical acceleration for the airplane to be zero because it is traveling at a constant velocity. But gravity is still acting on it. So shouldn't it still have an acceleration of g? Or does this have something to do with the fact that the airplane, not being like a projectile in that is has engines, is providing its own force? I find this rather confusing. It has been many years since I studied any physics and I keep scoring around 7 on the physics stuff. Could someone clear this up for me please. Link to comment Share on other sites More sharing options...
AdamP Posted June 14, 2009 Report Share Posted June 14, 2009 Looks like your reasoning is right, think of the FBD on a falling ball and a plane, the plane has a lift force acting opposite gravity so the NET a would be zero (there is still a gravity force in the vertical, it is just counter acted). The ball has no such lift force so its fbd would just have a vertical force down making the net a = g Question, if you knew the mass of the plane, how would you figure out what the lift force actually is? Link to comment Share on other sites More sharing options...
AG22 Posted June 16, 2009 Report Share Posted June 16, 2009 Question, if you knew the mass of the plane, how would you figure out what the lift force actually is? Would it be mg [up]? Link to comment Share on other sites More sharing options...
2011hope Posted June 16, 2009 Author Report Share Posted June 16, 2009 Looks like your reasoning is right, think of the FBD on a falling ball and a plane, the plane has a lift force acting opposite gravity so the NET a would be zero (there is still a gravity force in the vertical, it is just counter acted). The ball has no such lift force so its fbd would just have a vertical force down making the net a = g Question, if you knew the mass of the plane, how would you figure out what the lift force actually is? thanks for the help Link to comment Share on other sites More sharing options...
rmorelan Posted June 16, 2009 Report Share Posted June 16, 2009 Would it be mg [up]? Yup I love physics Link to comment Share on other sites More sharing options...
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