Calculate Cliff Height: Free-Fall Problem with Rock Dropped from a Cliff

[iMAGICIALoTV]

A rock dropped from a cliff falls one-third of its total distance to the ground in the last second of its fall. How high is the cliff?

I'm not asking for answer, I know the Physics Forum rules, but I am totally unsure where to start. I guess I have to use the equation d = V_ot + at²/2 ?

Could you please give me a hand and help me figure it out, please. Hints is all I need. Thanks.

 

[Draco27]

lemme try

you are given initial velocity =0
acceleration is 10/9.8m/s²
let total height be h
and time taken to cover full length be t+1 sec

now find distance traveled is t seconds and then find it for t+1 sec

then u get 2 equations involving time and height

solve for answers...

 

[iMAGICIALoTV]

Why t+1, though?

 

[Draco27]

now distance traveled in last sec is known

so u can take total time as t and 1 sec before time time as t-1

or

u can take total time as t+1 and 1 sec before time as t

 

[Bhumble]

Or just solve for V_0 with d = 1/3 h and t = 1 s. Then go back and solve for the time it takes to attain that velocity in free fall.

 

[rl.bhat]

h = 1/2*g*t^2 --------(1)
h - h/3 = 1/2*g*(t - 1)^2 -------(2)
Divide 1 by 2 and solve for t. Hence find h.