Chapter 9, Problem 38A

How many joules of potential energy does a 1-kg book gain when it is elevated 4 m? When it is elevated 8 m? (Let $g=10N/kg$.)

To determine

Potential energy gained by book.

Answer to Problem 38A

Potential energy gained by book 40 J and 80 J

Explanation of Solution

Given :

Mass of the book, $m=1\text{ kg}$

Height is given, $h_1=4\text{ m, }{h}_2=8\text{ m}$

Acceleration due to gravity, $g=10\text{ N/kg}$

Formula used :

Potential energy is given by,

  $PE=mgh$

Where, m is mass, g is acceleration due to gravity and h is height.

Calculation :

Now, substituting the value of m , g and $h=h_1$ and solve.

  $\begin{array}{l}PE=1\times 10\times 4\\ =40\text{ J}\end{array}$

For, $h=h_2$

  $\begin{array}{l}PE=1\times 10\times 8\\ =80\text{ J}\end{array}$

Conclusion :

Therefore, potential energy gained by book is 40 J when elevation is 4 m and potential energy is 80 J when height is 8 .