Kinematics Eq: Can F Be Changing?

[fball558]

Quick question??

Homework Statement

this is not really a problem just was wondering,
does the following Kenimatics equation only work when the
force is a constant or can i work when the F is changing?
the equation is the one relating acceleration to velocity as follows

V(final)^2 = V(inital)^2 + 2*a*d

i know you can find a by using F=ma
i used this problem a earlier to find final velocity of an orbiting planet.
i used F to be equal to the graviational attraction between the two objects
the whole

G* m1*m2/r^2 thing.

but not sure if that would work or not.
if you know or have an opinion let me know
thanks

 

[swraman]

Yes, that equation is derived under the assumption of constant acceleration, thus constant force.

If you want to find equations of motion for non-constant acceleration, you must start with F=ma and use calculus to solve for the desired quantity.