Science

PhysicsQ&A Library1. 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 Jmy?Kinetic 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/sec² isacceleration due to gravity; h is height (m).4.Work W (J):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 = FAxcose , where W is work, Ax is the displacement of the system, and e 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 = mvi – mvLet 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 7 of an energy conversion process isdefined as n =4, here v¡ is final velocity and v;is initial velocity.where W is useful energy or work output, E is total energy input, Q is heat or thermalw-Qenergy.8. Energy conversion in humansWOur own bodies, like all living organisms, are energy conversionmachines. Conservation of energy implies that the chemicalenergy stored in food is converted into work, themal 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 K, = 17,2 kJ/g =4.11 Cal/gfat K2 = 38,9 kJ/g = 9.3 Cal/g.(negative)WorkOE,FoodThermalenergyenergyOE,StoredfatOE, + W- OE, 9. Metabolic rate for selected activitiesThe amount of energy consumed by a person depends on the person's weight and build. It has been found,however, that the amount of energy consumed by a person during a given activity divided by the surfacearea of the person's body is approximately the same for most people. Therefore, the energy consumed forvarious activities is usually quoted in Cal/m-hr. This rate is known as the metabolic rate.10. Energy consumption E = MR · A t,here MR is metabolic rate (Calm? hr), A is surface area(m³) and t is time (sec).11. Surface area of body A (m?):A = 0,202m0425 H0,725 here m is the weight of the personin kilograms, and H is the height of the person in meters.Metabolic rate(Calm'-hr)ActivitySleepingLying awakeSiting uprightStandingWalking (3 mph)Moderate physical workBicyclingRunningShivering35405060140150250600250Question

Asked Feb 12, 2020

1 views

Using data from Table, calculate the daily energy needs of a person who sleeps for 8.00 h, walks for 2.00 h, works in the office for 8 hours, does moderate physical work during 2 hours and lying awake for 4 hours. (suppose, that working in office consumes energy at the same rate as sitting upright.). Suppose that the person mass is 80-kg and his height 1.75m.

Step 1

The surface area of the person is found as,

...

Tagged in

Find answers to questions asked by student like you

Show more Q&A

Q: b. Find an expression for the particle's velocity ỷ as a function of time. c. What is the particle's...

A: Click to see the answer

Q: Can i get help with problem step by step?

A: Since we are entitled to answer up to 3 sub-parts, we’ll answer the first 3 as you have not mentione...

Q: The sound intensity of a conversation at a distance of 5.0 m is 1.7 x 10-7 W / m^2 . Determine the i...

A: Click to see the answer

Q: Determine the amount of work needed to assemble the following charges from infinity: Q1 = +70 mC at ...

A: Click to see the answer

Q: A 2.0 kg block travels around a 0.50 m radius circle with an angular velocity of 13 rad/s. The magni...

A: Angular momentum,

Q: A bird watcher meanders through the woods, walking 1.42 km due east, 0.267 km due south, and 4.04 km...

A: The details given can be demonstrated as

Q: help me double check your answers last 3 tutors got it wrong. i attached the correct answer for part...

A: a. The net force acting along x axis is zero. Then write the expression for net force in the x dire...

Q: #12 with explanation

A: According to coulomb’s law the force between two charges is directly proportional to magnitude of th...

Q: Chapter 04, Problem 029 7 Your answer is partially correct. Try again. The drawing shows three parti...

A: Click to see the answer