Basic kinetmatic problem

[ahs4n]

Suppose that a ball is thrown vertically upward from earth with velocity v, and returns to its original height in a time t. If the value of g were reduced to g/6 (as on the moon), then t would:

My first instinct was to use the equation

change in y= vt + 1/2at^2

instead, the test says to use v = v + at

What should I change in my thinking to make sure that I know to use the second equation?

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[joshinjosh]

y = vt+1/2at^2 contains an additional variable, y. y is not the same in both situations so vf = vo + at requires less work. You can use y = vt+1/2at^2, but this will require additional steps to solve for y and you will basically come back alongs the lines of the vf = vo + at equation.

I find the best way to decide which kinematic equation to use is to look at the all variables of the question and then to choose the simpliest equation(s) that contains all the variables.

hope this helps,

Josh

 

[ahs4n]

Thanks that helps a lot.... I forgot that if gravity increased or decreased that the distance would also change. I was accounting that the distance stayed the same no matter what.