How long can a Snickers bar power the human brain?

In summary, the human brain typically consumes 21.9 W of power, but may require more during exams. Using the conversion factor between calories and joules, one Snickers bar with 280 cal can power the brain for approximately 53.52 seconds. However, this answer is incorrect due to a mistake in the conversion. The actual answer would require eating about 60 Snickers bars to sustain brain function during an exam.
  • #1
UCrazyBeautifulU
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The human brain consumes about 21.9 W of power under normal conditions, though more power may be required during exams. How long can one Snickers bar (280 cal per bar) power the normally functioning brain?[/B] (Note: The nutritional calorie, 1 Cal, is equivalent to 1000 calories (1000 cal) as defined in physics. In addition, the conversion factor between calories and joules is as follows: 1 Cal = 1000 cal = 1 kcal = 4186 J.)

I keep getting the answer 53.52 seconds after I do the conversion and use the formula P = W/t

However, 53.52 seconds isn't the correct answer (LON CAPA did not accept it), anyone else have any ideas on this one?
 
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  • #2
You did the problem almost correctly. Read carefully that a food calorie is actually 1000 calories.

Also, think about the 53.52 seconds for a brain to run on a snickers bar; you'd need to eat about 60 of them just to make it through an exam at that rate :) The actual answer makes more sense.
 
  • #3
You are off by an order of magnitude. How many Joules of energy is stored in that Snickers bar?
 
  • #4
thanks so much, you guys really helped me out! I knew it didn't make sense, but I couldn't figure out what I was doing wrong.
 

1. What is the definition of work in physics?

In physics, work is defined as the transfer of energy from one object to another by the application of a force. It is measured in joules (J) and is calculated by multiplying the force applied by the distance over which the force is exerted.

2. How is work related to kinetic energy?

Work and kinetic energy are closely related because work done on an object can change its kinetic energy. When a force is applied to an object and it moves through a distance, work is done on the object, resulting in a change in its kinetic energy.

3. Can work be negative in a work and kinetic energy problem?

Yes, work can be negative in a work and kinetic energy problem. This happens when the force and displacement are in opposite directions, resulting in the work being done against the direction of motion. Negative work decreases the object's kinetic energy.

4. What is the work-energy theorem?

The work-energy theorem states that the net work done on an object is equal to the change in its kinetic energy. In other words, the work done on an object will result in a change in its kinetic energy, whether it is an increase or decrease.

5. How can I solve a work and kinetic energy problem?

To solve a work and kinetic energy problem, you can use the formula W = Fd to calculate the work done on the object. Then, use the formula KE = 1/2mv^2 to calculate the initial and final kinetic energies. Finally, apply the work-energy theorem to find the change in kinetic energy and solve for the unknown variable.

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