Question

A book on a 2-meter high shelf has a mass of 0.4 kg. What is its potential energy?

Answer 1

7.84 is your answer ok bye

Answer 2

`\boxed {\boxed {\sf 7.84 \ Joules}}`

Step-by-step explanation:

The formula for potential energy is:

`PE=m*g*h`

where m is the mass, g is the gravitational acceleration, and h is the height.

The mass of the book is 0.4 kilograms. The gravitational acceleration on Earth is 9.8 m/s². The height of the book is 2 meters.

`m=0.4 \ kg \\g=9.8 \ m/s^2 \\h=2\ m`

Substitute the values into the formula.

`PE=(0.4 \ kg)(9.8 \ m/s^2)(2 \ m)`

Multiply the first two numbers.

• 0.4 kg*9.8 m/s²= 3.92 kg*m/s²
• If we convert the units now, the problem will be much easier later on.
• 1 kg*m/s² is equal to 1 Newton. So, our answer of 3.92 kg*m/s² is equal to 3.92 N

`PE=(3.92 \ N )(2 \ m)`

Multiply.

• 3.92 N* 2 m=7.84 N*m
• 1 Newton meter is equal to 1 Joule (this is why we converted the units).
• Our answer is equal to 7.84 Joules.

`PE=7.84 \ J`