2. A firefighter feels the hose pushing backwards onto him as he uses it to put out a fire. What is the most likely cause of this?
A. The hose material is very elastic.
B. Since the hose is at rest, it tends to stay at rest.
C. The force exerted on the water equals the mass of the water times its acceleration
D. The escaping water exerts an equal and opposite force on the hose.

D. The escaping water exerts an equal and opposite force on the hose.

Explanation:

To be able to solve this question we must know that the firefighter is in balance, that is, he feels some forces when using the hose, but these forces do not make him move.

Let's analyze each of the answers:

A. The hose material is very elastic.

The forces are felt at the hose outlet and independent of the rigidity of the hose, the force is a function of the outlet speed and the outlet area of the hose

B. Since the hose is at rest, it tends to stay at rest.

The hose is in balance not at rest, and is in balance due to the force exerted by the fireman.

C. The force exerted on the water equals the mass of the water times its acceleration.

This is the definition of Newton's second law, and it is useful for moving bodies. But for this case it does not apply since there is no movement, the fireman grabs the hose in such a way that there is a balance.

D. The escaping water exerts an equal and opposite force on the hose.

This is the answer, and corresponds to Newton's third law, the fundamental principle of Statics studies. This law tells us that every force applied on a body corresponds to an equal and opposite force in the opposite direction. Just like when we try to push a wall, the wall exerts an equal force and in the opposite direction. The balance would be interrupted in this case when the speed of water outflow is so great that the fireman's strength is not enough to maintain balance.

  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

well, you would divide 135 by 33 to get your answer. then that is how many seconds it would take. boardman should fly about 132 m or 4.090909090909091 seconds.