Question

A rock is thrown upward with a velocity of 15 meters per second from the top of a 34 meter high cliff, and it misses the cliff on the way back down. When will the rock be 3 meters from the water, below? Round your answer to two decimal places.

Answer 1

At 4.47 seconds rock will be 3m meters from the water.

Step-by-step explanation:

We need to find when will the rock be 3 meters from the water.

That is rock has traveled (34-3) meters below.

Displacement = 31 m

Since the displacement is along down we need to give negative sign.

Displacement = -31 m

Initial velocity = 15 m/s

`\texttt{Acceleration}=-9.8m/s^2 \\`

We have equation of motion

`s=ut+(1)/(2)at^2 \\`

Substituting

`-31=15t-(1)/(2)* 9.81* t^2\\\\4.9t^2-15t-31=0\\\\t=4.47\texttt{ or }t=-1.41 \\`

Neglecting negative time.

time, t = 4.47 seconds.

So at 4.47 seconds rock will be 3m meters from the water.