7. if the acceleration due to gravity is -9.8 m/s2
a. how long will it take a freely falling body to acquire a speed of 58.8 m/s?

6 s

Explanation:

Since the motion of an object in free fall is a uniformly accelerated motion, we can use the following suvat equation:

v = u+at

where

v is the velocity after a time t

u is the initial velocity

is the acceleration of gravity

Assuming the body is dropped from rest (so, u = 0), therefore, the equation becomes

So, the time t at which the velocity becomes -58.8 m/s is

So after 6 s, the velocity of the body is -58.8 m/s, where the negative sign indicates the downward direction. Since the speed is just the magnitude of the velocity, this means that the speed of the body after 6 s will be 58.8 s.

28. evolution

29. environment, survive, offspring  

explanation:

  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