Question

1) A rock with a mass of 550 g in air is found to have an apparent mass of 327 g when submerged in water.

a) What mass, in grams, of water is displaced?

b) What is the volume, in cubic centimeters, of the rock?

c) What is the average density of the rock, in grams per cubic centimeter?

2) Suppose 1.95 L of gas at 37°C is under 7.37 × 107 Pa of pressure. How many moles of gas are there in the system?

3)Suppose a woman does 350 J of work and 9400 J of heat is transferred from her into the environment in the process.

a) What is the change in her internal energy, in joules, assuming she does not consume any food?

b) What is her percent efficiency?

Answer 1

a) It will displaces 327g of water

b) 327g of rock will submerged completly when its density is 1/ 4 of water.

   density of water is 1g/ cm³ . so the density of rock will be three quarter when it is submerged which will be

   o.75g /cm³

The volume will be = V= mass / density = 327g / o.75g /cm³ = 436cm³

Average density will be found by average mass = (550g + 527g ) / 2 = 1077g

                     Average density = 1077 g / 436cm³ = 2.47g / cm³

2) Using ideal gas equation

            PV = nRT

           n = PV / RT

        R = gas constant = 8.3 J / k . mol

       Putting the values of Prassure , VOlume , Gas constant (R) and Temprature you can determine the value of number of moles.

3)   From ist law of thermodynamics

               Q = dE + W

              dE = Q - W

              dE = 9400 - 350

              dE = 9050 J

b) Percent efficicency = output / input ( 100%)

                                = (350 / 9400) 100%

                                  = 3.7%