Hi there, I'm taking first year physics right now and I have two homework questions that I am unable to get. If anyone would be able to show me how they got the answer, I would be most grateful! The first one is on power and the second one is on electricity.
1) The human body has an efficiency of about 30% in converting the energy in food consumed into useful work. How much protein, which supplies 17 MJ/kg, must be consumed by a 75 kg boy to provide the energy needed to climb a set of stairs rising 180 m?
The answer is 26 g
and
2) A carbon atom contains 6 protons and 6 neutrons in its nucleus, and 6 electrons around its nucleus. A piece of carbon with a mass of 12.0 g contains 6.0 x 10(to the 23rd power) atoms. If each atom in a 1.0 g piece of carbon lost one electron, what would be the charge on the carbon?
The answer is +8.0 x 10(to the 3rd power) C. I don't know if this is important but electrons have a charge of -1.6 x 10( to the -19th power) C.
So as you see, I know the answer but have no idea how to achieve it! Thank you so much for your help.
1) The human body has an efficiency of about 30% in converting the energy in food consumed into useful work. How much protein, which supplies 17 MJ/kg, must be consumed by a 75 kg boy to provide the energy needed to climb a set of stairs rising 180 m?
The answer is 26 g
and
2) A carbon atom contains 6 protons and 6 neutrons in its nucleus, and 6 electrons around its nucleus. A piece of carbon with a mass of 12.0 g contains 6.0 x 10(to the 23rd power) atoms. If each atom in a 1.0 g piece of carbon lost one electron, what would be the charge on the carbon?
The answer is +8.0 x 10(to the 3rd power) C. I don't know if this is important but electrons have a charge of -1.6 x 10( to the -19th power) C.
So as you see, I know the answer but have no idea how to achieve it! Thank you so much for your help.
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Okay, here's number 1.
Of course, you're assuming there are no friction losses between sneakers and stairs, or drag from air resistance since once you factor those in it gets more complicated.
The amount of work/energy needed to go against gravity is mass x acceleration (the acceleration the boy would undergo in a free fall) x vertical distance.
Energy needed = 75kg * 9.8 m/s/s * 180m = 132,300 Newton-meters, or Joules. This equals 0.1323 MJ.
Now divide by 0.3 (the efficiency) to get the total amount of energy he would need from the food. Some of the food is turned into useful energy, but the rest gets turned into body heat.
He needs 0.441 MJ from food.
Now divide by 17 MJ/kg to get 0.0259 kg protein, or 25.9 grams (about 1 ounce). He would have needed to eat the same amount of starch or sugar, but only 11.5 grams of fat to go the same distance.
Number 2:
(6.022 x 10^23)/12 * -1.6 *10^19 = -8,000 Coulombs lost, so the remaining carbon has a positive charge of 8,000 C
Of course, you're assuming there are no friction losses between sneakers and stairs, or drag from air resistance since once you factor those in it gets more complicated.
The amount of work/energy needed to go against gravity is mass x acceleration (the acceleration the boy would undergo in a free fall) x vertical distance.
Energy needed = 75kg * 9.8 m/s/s * 180m = 132,300 Newton-meters, or Joules. This equals 0.1323 MJ.
Now divide by 0.3 (the efficiency) to get the total amount of energy he would need from the food. Some of the food is turned into useful energy, but the rest gets turned into body heat.
He needs 0.441 MJ from food.
Now divide by 17 MJ/kg to get 0.0259 kg protein, or 25.9 grams (about 1 ounce). He would have needed to eat the same amount of starch or sugar, but only 11.5 grams of fat to go the same distance.
Number 2:
(6.022 x 10^23)/12 * -1.6 *10^19 = -8,000 Coulombs lost, so the remaining carbon has a positive charge of 8,000 C