Question

Additional info:

Meal = 1720 Kilocalories

Mass of myself = 50 kg

The Joule () is the SI unit of energy. (J = kg:m? S2 A calorie is another unit of energy. The definition of a calorie is the amount of heat (energy) necessary to raise the temperature of Ig of water by 1° Celsius. Ig of water occupies 1 milliliter (ml) = 1 cubic centimeter (cm) of volume. lkcal=4186J Energy comes in many forms and energy may be converted from one form to another. In the following problems, assume all the energy stored in the food is converted to the type of energy specified. None is lost to other forms in the process (even though this is unrealistic). You will need to choose a mass for yourself. If you don't want to tell your tell your true mass then use 50kg or 100kg. 1. How many liters of water can you heat from room temperature to boiling using the energy stored in the above meal (food energy becomes thermal energy)? 2. If all the energy stored in the meal were used to raise you to the top of a mountain, how high would the mountain be (food energy becomes gravitational potential energy)? (gravitational potential energy)=(mass)>(gravity)x(height) U = mgh [For comparison, Mt. Everest is 8,850 meters above sea level] 3. If all this energy were used to make you move, how fast would you be going (food energy becomes kinetic energy)? 1 K = -my? (kinetic energy) = -5x (mass)x(speed) [For comparison, the speed of sound is about 343 m/s in air.] 4. If the coefficient of friction were 0.5, how much distance would you need to stop if you were moving the above speed (kinetic energy lost is work due to friction)? (change in kinetic energy) = -(frictional force) (displacement) AK =-fax 5. Based on the answers to the previous four questions, do you think more of the food energy that you consume goes into heat or motion? 6. Roughly, how fast can you run? (There are meter sticks and timers for you to go outside and estimate your running speed if you need them.) How many kilocalories worth of kinetic energy would this be? 7. What is the greatest change in elevation (in meters) that you have ever achieved in one day while walking? (Backpacking, climbing stairs in tall buildings, ...) How many kilocalories would this change in potential energy correspond to?

Answer 1

Meal = 1720 Kilocalories Mass of myself = 50 kg 1. Energy = Q = 1720 Kilo calories 1 kilo cal = 4186 J then Q = 1720 (4186 J) = 7199920 J specific heat of water = Cw = 4186J/kg degree C change in tempearture = boiling point of water – room tempeartue AT = 100 degree C - 20 degree C = 80 degree C formula Q= m, .CAT water

m Q CAT water m water 7199920J 4186J/kg degree CX 80 degree m "water = 21.5kg so, water required as 21.5 kg Ans. 2. mass of the person = m = 50 kg E = mgh

E h= mg h= 7199920J -=14693.71 m 9.8m/s-x50 kg This is larger than the heigh of the everest. 3. if E = K = 1 2 7199920J = (50 kg)v? 7199920J=(25 kg) v? 7199920J_(25 kg) -V4 25 kg 25 kg

v2 =287996.8 v=287996.8 v=536.7 m/s 4. since, it starts from rest, so, initial velocity = 0 so, initial kinetic energy = Ki = 0 final kinetic energy Kf = E = 7199920 J

change in kinetic energy = Kf - Ki = 7199920 J friction force is defined as, f= Ukmg m = mass of the person and g = acceleration due to gravity then, Kf - Ki = -fd Kf - Ki = ukmg d 7199920 J (0.5)(50kg)(9.8 m/s^2) d d = 29387.42 m Ans