Question

a 10-kg rock falls from a height of 8.0 m above the ground. what is the kinetic energy of the rock just before it hits the ground?

320 j

80 j

98 j

780 j

Explanation:

Step1: Identify potential energy formula

Gravitational potential energy: $PE = mgh$

Step2: Substitute given values

$m=10\ \text{kg}$, $g=9.8\ \text{m/s}^2$, $h=8.0\ \text{m}$
$PE = 10 \times 9.8 \times 8.0$

Step3: Calculate energy conversion

Kinetic energy equals lost potential energy: $KE = PE$
$KE = 784\ \text{J} \approx 780\ \text{J}$

Answer:

780 J