Question

test information
description: show all you work, including units, on separate paper. follow the \problem solving method\. this final exam is cumulative and covers material from the entire course.
instructions: from the list of choices, select the one best answer.
multiple attempts: not allowed. this test can only be taken once.
force completion: this test can be saved and resumed later. your answers are saved automatically.
question completion status: list of question numbers
question 14
1.6 points
a pebble is dropped from the top of a tall cliff and strikes the ground 2.8 s later. how tall is the cliff?
○ 49 m
○ 38 m
○ 65 m
○ 72 m

Explanation:

Step1: Identify the motion type

The pebble is in free - fall, so we use the kinematic equation for free - fall displacement: $h=\frac{1}{2}gt^{2}$, where $g = 9.8\ m/s^{2}$ (acceleration due to gravity) and $t$ is the time of fall.

Step2: Substitute the values

Given $t = 2.8\ s$ and $g=9.8\ m/s^{2}$, we substitute into the formula:
$h=\frac{1}{2}\times9.8\times(2.8)^{2}$
First, calculate $(2.8)^{2}=7.84$. Then, $\frac{1}{2}\times9.8 = 4.9$. Then, $h = 4.9\times7.84$.
$4.9\times7.84=(5 - 0.1)\times7.84=5\times7.84-0.1\times7.84 = 39.2-0.784 = 38.416\approx38\ m$

Answer:

38 m (corresponding to the option "38 m")