Projectile Motion From Cliff Homework: Solving for Distance and Time

[crazskier29]

Homework Statement

A projectile is launched with speed v0 making angle θ0 with the horizontal from the edge of a vertical cliff at height Q above a horizontal plane. At what distance from the bottom of the cliff does the projectile land?

Homework Equations

v0x=v0cosθ0
v0y=v0sinθ0
deltax=v0sinθ0*t
deltay=v0sinθ0*t
Q=v0sinθ*t-(gt^2)/2

equations that may work?
(v0)^2=vf^2+2ax... ?

The Attempt at a Solution

other than the equations above, I have not been able to solve anything. Basically, I need t to find delta x (the distance from the base of the clifff) and I know that i need to find t in terms of y (but that t in x and y are equal, but motion in x and y is independent)... according to my TA, i cannot assume that vfy=0 and that i must assume that it is just before it hits the ground. How do I find vfy with this assumption (as doing it with this assumption is easy)

Thanks! I have a final on monday 0_o

 

[Delphi51]

deltay=v0sinθ0*t is not correct; need to add g*t²
but I don't think you need this anyway.

Just solve your Q=v0sinθ*t-(gt^2)/2 for t.
Sub in deltax=v0sinθ0*t to get the final answer.