Chapter 9, Problem 50A

A stuntman on a cliff has a PE of 10,000 J. Show that when his potential energy is 2000 J, his kinetic energy is 8000 J.

To determine

To show: Kinetic energy is 8000 J at given potential energy

Explanation of Solution

Given:

When stuntman is on the cliff, $P{E}_1=10000\text{J}$

New potential energy is $P{E}_2=2000\text{J}$

Formula Used:

According to energy conservation,

Initial energy = Final energy

Calculation:

At cliff height $K{E}_1=0$ since, stuntman is at rest.

From the conservation of energy, change in energy is zero. So,

Initial energy = Final energy

  $\begin{array}{l}K{E}_1+P{E}_1=K{E}_2+P{E}_2\\ \Rightarrow 0+10000=K{E}_2+2000\\ \Rightarrow K{E}_2=10000-2000=8000\text{J}\end{array}$

Conclusion:

Therefore, it is proved that when potential energy is 2000 J, kinetic energy of stuntman is 8000 J