Which of these physical settings makes sense for an object moving along the x-axis? its position at any time is given by x(t) = 3cos(π t) + 2
a. a skydiver falling from a plane, before she opens her parachute.
b. the shadow cast by a rock that's stuck on the edge of a spinning wheel.
c. a car driving from san diego to los angeles.
d. an ant walking at a steady pace from the tip of a propeller toward the hub.
e. none of these settings.

option b is correct.

Explanation:

Since the position as a function of time is given by

which is a periodic function thus the motion of the particle repeats after a time of 2 seconds thus among the given options only option b is case of repetitive motion thus option b is most appropriate since the spinning wheel repeates it's motion.

  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

there are no contact forces mentioned on the list of choices that you've provided.