Question

Assume chemical energy from food can be extracted through digestion and respiration within the body and the efficiency in converting this energy into mechanical energy is 18%. How much chemical energy from food should a student consume in order to lift a 15 kg mass 1.5 m and repeat this activity 500 times?

Answer 1

`612,500J`

Step-by-step explanation

The efficiency in converting chemical energy to mechanical energy is 18%. This implies that 0.18 of chemical energy is converted to mechanical energy.

Let the amount of chemical energy be x.

Let the amount of mechanical energy be y.

Hence:

`0.18x=y`

The mechanical energy required to lift a 15 kg mass 1.5 m is the potential energy i.e.:

`PE=mgh`

where m = mass; g = acceleration due to gravity; h = height

Therefore, we have that:

`\begin{gathered} PE=15\cdot9.8\cdot1.5 \\ PE=220.5J \end{gathered}`

If the activity is repeated 500 times, the energy required is:

`\begin{gathered} y=220.5\cdot500 \\ \Rightarrow y=110,250J \end{gathered}`

Recall that:

`0.18x=y`

This implies that the chemical energy that the student must consume is:

`\begin{gathered} x=(y)/(0.18) \\ x=(110250)/(0.18) \\ x=612,500J \end{gathered}`