PHYSICS
posted by HELP .
You accidentally throw your car keys horizontally at 10.0 m/s from a cliff 78 m high. How far from the base of the cliff should you look for the keys?

how much time does it take to fall 78m?
hf=1/2 g t^2
78=1/2 9.8 t^2 solve for t.
how far horizontally? distance= 10m/s * time 
The time required fir the keys to to fall H = 78 m is
T = sqrt(2H/g) = 3.99 seconds.
Multiply that by the initial velocity, which remains the constant horizontal velocity component during the fall to the ground below.