Question

. A rock is dropped from a height of 4 m. How fast is it going when it hits the ground? The rock has a mass of 2 kg. (Hint: MEi = MEf)

Answer 1

Answer:

8.85 m/s

Explanation:

Answer 2

Hello!

When the rock is dropped, it only contains Gravitational Potential Energy, and when it hits the ground, it contains Kinetic Energy.

So:

PE = KE
$\large\boxed{mgh = \frac{1}{2}mv^2}$

We can rearrange to solve for velocity. Cancel out mass and solve.

$gh = \frac{1}{2}v^2\\\\2gh = v^2\\\\v = \sqrt{2gh}$

Plug in the givens:

$v = \sqrt{2(9.8)(4)} = \boxed{8.85 \frac{m}{s}}$