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PhysicsQ&A Library2. Using data from Table, calculate the daily energy needs of a person who sleeps for 8.00 h, walksfor 2.00 h, works in the office for 8 hours, does moderate physical work during 2 hours and lying awakefor 4 hours. (suppose, that working in office consumes energy at the same rate as sitting upright.). Supposethat the person mass is 80-kg and his height 1.75m. 1. First law of thermodinamics AQ = AU + AWThe first law of thermodynamics is a version of the law of conservation of energy The first law is oftenformulated by stating that the change in the internal energy AU of a closed system is equal to the amountof heat supplied to the system AQ, minus the amount of work done AW by the system on itssurroundings.Units of work and energy are Joules(J) and calories (cal).Relationship between units 1 cal = 4.18 J and 1 Cal = 1000 cal = 4180 JKinetic energy (J): KE = , here m is mass of a body (kg), v – speed of its motion(m/sec).2.3. Gravitational potential energy(J): PE = mgh, here m is mass of the body (kg); g = 9,8 m/sec? isacceleration due to gravity; h is height (m).Work W (J):4.Formally, the work done on a system by a constant force is defined to be the product of the componentof the force in the direction of motion times the distance through which the force acts. For one-way motionin one dimension, this is expressed in equation form as:W = FAxcos0 , where W is work, Ax is the displacement of the system, and 6 is the angle between theforce vector F and the displacement vector Ax.5. Work – Energy theorem: The principle of work and kinetic energy (also known as the work-energytheorem) states that the work done by the sum of all forces acting on a particle equals the change in thekinetic energy of the particle: W = AKE = "-i, here v, is final velocity and v; is initial velocity.Let us calculate the work done in lifting an object of mass m through a height h. If the object is liftedstraight up at constant speed, then the force needed to lift it is equal to its weight mg. The work done onthe mass is: W = APE = mgAh, here m is mass of the body (kg); g = 9,8 m/sec? is acceleration due togravity; Ah is change in height.6. Power P (W) is rate at which work is done: P = ", where W is work (J) and t is time.7. Efficiency Even though energy is conserved in an energy conversion process, the output of usefulenergy or work will be less than the energy input. The efficiency n of an energy conversion process isdefined as 1 =- where W is useful energy or work output, E is total energy input, Q is heat or thermalw-Qenergy.8. Energy conversion in humansOur own bodies, like all living organisms, are energy conversionmachines. Conservation of energy implies that the chemicalenergy stored in food is converted into work, thermal energy,and/or stored as chemical energy in fatty tissue. The fractiongoing into each form depends both on how much we eat and onour level of physical activity. If we eat more than is needed todo work and stay warm, the remainder goes into body fat.carbohydrates and proteins K1 = 17,2 kJ/g =4.11 Cal/gfat K2 = 38,9 kJ/g=9.3 Cal/g.W (negative)WorkOEFoodThermalenergyenergyOE,StoredfatOE, + W = OE,Question

Asked Jan 23, 2020

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Step 1

The table shows the energy consumption rate for various activities:

Step 2

The energy used by the person while sleeping for 8.0h is,

Step 3

The energy used by the person wh...

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