Arock is dropped from the top of a vertical cliff and takes 3.00 s to reach the ground below the cliff. a second rock is thrown vertically from the cliff, and it takes this rock 2.00 s to reach the ground below the cliff from the time it is released. with what velocity was the second rock thrown, assuming no air resistance?
a) 12.3 m/s upward
b) 4.76 m/s downward
c) 4.76 m/s upward
d) 12.3 m/s downward
e) 5.51 m/s downward

D) 12.3 m/s downward

Explanation:

We use the next free fall equation

where is the height of the cliff, the initial velocity, the acceleration of gravity () and is time.

For the fist rock since the rock was dropped, and , so we have:

simplifying

the height of the cliff is 44.145m

Now, about the second rock we know that is the same height and now the time es , and we need to find

From the fist equation

we clear for

and substitute known values

wich rounds up to

the direction is downward because the rock is thrown so that it falls through the cliff.