Acar travels down a straight road. which of newton's laws must be put into effect to cause the car to follow a curve in the road

That would be Newtons 3rd law of motion.

Netwon's first law of motion

Explanation:

This is also known as law of inertia and its states that " a body will remain at rest or in a state of constant motion along a straight line unless acted upon by another force". I.e to say that a body will remain in a straight line unless an external force acts to change its direction.

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-