Question

You release a pendulum of mass 1 kg from a height of 0.75 m. If the pendulum loses 18% of its initial energy by the time it reaches the bottom, how fast is it going when it reaches the bottom?

Answer 1

ANSWER:

3.47 m/s

STEP-BY-STEP EXPLANATION:

We can calculate the velocity value assuming that the kinetic energy is equal to potential, therefore:

$\begin{gathered} PE=KE \\ mgh=\frac{1}{2}mv^2 \end{gathered}$

By losing 18% of initial energy, it means that the energy value is 82% (100-18), which means that the speed also represents 82%.

We replace the values and calculate for v, like this:

$\begin{gathered} 0.82\cdot mgh=\frac{1}{2}mv^2 \\ v=\sqrt[]{2gh} \\ v=\sqrt[]{0.82\cdot2\cdot9.8\cdot0.75} \\ v=3.47\text{ m/s} \end{gathered}$