You have two photos of a person walking. One shows the person at the corner of Third and Main streets, the other shows the person at the corner of Tenth and Main streets. There are lampposts at every corner in this town, and the first picture shows it to be 10:32:00 exactly. The second picture shows it to be 10:49:30. You know three facts: (1) All of the clocks are synchronized; (2) there are exactly 12 equal-sized blocks per kilometer in this town; and (3) the streets that cross Main in this area are numbered consecutively, with no interruptions. What is the person’s average speed in kilometers per hour?

average speed

= [(10-3)/12 km] / [(49.5-32.0)/60 hour]

= 5*7 / 17.5

= 2 km/h .

  the grams     of oxygen gas   that can be produced     is 20.6   grams of o₂

calculation

2liclo₃ →   2 licl + 3 o₂

step 1:   find the moles of liclo₃

moles = mass÷ molar mass

from periodic table the molar mass of liclo₃ =6.9 +35.5   +(16 x3) =90.4 g/mol

moles=38.7 g÷90.4 g/mol=0.4281   moles

step 2:   use the   mole ratio   to calculate the moles of o2

from equation above, liclo₃: o₂   is 2: 3  

therefore the moles of   o₂=0.4281 moles x3/2 =0.6422   moles

step 3: find mass   of o₂

mass= moles x molar mass

from periodic table the   molar mass of   o₂ = 16 x2= 32 g/mol

mass=0.6422   moles   x   32 g/mol = 20.6 grams of o₂

find the surface area of the sphere to the nearest square unit. use a calculator.

a. 254 in.2

b. 64 in.2

c. 127 in.2

d. 1,018 in.2