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

Answer:

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

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

$s=ut+\frac{1}{2}at^2$

Substituting

$-31=15t-\frac{1}{2}\times 9.81\times t^2\\\\4.9t^2-15t-31=0\\\\t=4.47\texttt{ or }t=-1.41$

Neglecting negative time.

time, t = 4.47 seconds.

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