How Efficient Are Human Leg Muscles?

[coconut62]

Please refer to the image attached.

For Q5, I did it like this:

Output energy = (50kg x 10 x 0.35metre) x 30times x 4minutes

And divide the answer by 120kJ.

The percentage I got is 17.5 Joules but the answer is 15J.

Did I do anything wrong?

For Q6, the temperature should fall, correct?

Thanks in advance.

 

[ehild]

The muscles did work and produced heat. So the input energy is work+heat. The efficiency is output energy divided by input energy.

ehild

 

[coconut62]

But there are no informations about heat.

 

[ehild]

But there are no informations about heat.

Read the problem text: "The muscles generate 120 kJ heat".

ehild

 

[Nickie]

For Q5, it looks like you have correctly calculated the output energy, but you may have made a mistake in converting from Joules to kJ. 17.5 Joules is equal to 0.0175 kJ, which is closer to the given answer of 15J. Double check your conversion calculations to make sure they are accurate.

For Q6, yes, the temperature should fall as the muscles are working to produce energy and releasing heat. This is due to the law of conservation of energy, which states that energy cannot be created or destroyed, only transformed from one form to another. In this case, the chemical energy stored in the muscles is being transformed into mechanical energy (movement) and heat energy. As the heat energy is released, the temperature will decrease.