# Question 49-Chemical and Physical Foundations of Biological Systems Practice Test for the MCAT

If a nurse eats a dark chocolate bar which gives about $$70$$ kcal, what would be the distance needed by the nurse to burn all of the calories? (You may consult the attachment.)

Work and energy are two related concepts in physics and both are present when an object with a certain mass is being moved after applying force. If an object is at rest, a force needs to be applied in order to move it. Work is done when the object is being moved, and the energy refers to the measure of the ability to do work. Also, the work done during a determined amount of time can be calculated, which is called power.

The most common units used are:

Work: joule(J)
Energy: joule(J), kilocalorie (kcal)
1 kcal = 4184J
Power: watt (W)

When talking about energy, there are two types: kinetic energy and potential energy. If both are added together, the mechanical energy acting on an object or body can be calculated. The kinetic energy refers to the energy acting on a body in motion, while the potential energy refers to the energy action on a body due to gravity.

The formulas used to calculate work and mechanical, kinetic, and potential energy are:

ME = Mechanical energy = KE + PE
KE = Kinetic energy = $$\frac{1}{2}mV^2$$
PE = Potential energy = mgh
Work = Force $$\cdot$$ distance

The human body requires energy to do work (which is done by the muscles); that energy is given by the food we consume every day. For example, a 60 g bar of dark chocolate can give a total amount of energy of 280 kcal. When doing calculations of the energy used from food, it is important to remember that the human body has an energy efficiency of 25%, meaning that most of the energy that the body gets from food is not used.

A 20 kg wheelchair with a 60 kg patient is being pushed by a nurse, covering a distance of 10 m. The force required to move the wheelchair is equal to 400 N.

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