What is the height of the cliff?

[adidab12]

1. To determine how high a cliff is, a llama farmer drops a rock, and then 0.800 s later, throws another rock straight down at a velocity of −10.0 m/s. Both rocks land at the same time. How high is the cliff?




2. I know some kinematics equations must be used



3. I am stumped because I don't know the final velocity the height or the time just the difference in time between the two

 

[rl.bhat]

1. To determine how high a cliff is, a llama farmer drops a rock, and then 0.800 s later, throws another rock straight down at a velocity of −10.0 m/s. ]

What is your sign convention? Why the velocity is negative?

 

[adidab12]

i don't know what you mean by sign convention but velocity is negative because it is traveling downwards

 

[rl.bhat]

i don't know what you mean by sign convention but velocity is negative because it is traveling downwards

In that case, what is the direction of acceleration due to gravity, g?

 

[adidab12]

-9.8

 

[fallen186]

d=d₀+v*t+1/2at²
d=d₀+v*(t-.800s)+1/2a(t-.800s)²

First rock,
d₀=0
V=0
a=9.81
d=1/2at²

Second rock,
d₀=0
d=10m/s*(t-.800s)+1/2*9.81*(t-.800)²

I used calculator to find when these to intersect.
y₁=1/2at²
y₂=10m/s*(t-.800s)+1/2*9.81*(t-.800)²
Calc->Intersect
I got x =2.26sec y = 25.02 m