When a substance has changed into something new or different so that the original substance is gone, as in digestion, radioactive decay, or a battery in a flashlight producing light, it is known as a .

a. physical property
b. chemical property
c. physical change
d. chemical change

d . chemical change.

Explanation:

Physical change involves change which can be retrieved back . sugar is dissolved in water . It is physical change . because sugar can be retrieved by evaporating water.

burning of coal is a chemical change because the ash that we get after burning coal can not be turned into coal .

In the given case in the problem , after digestion , things that  are formed are  quite different . After radioactive decay new element is produced . In battery , current is produced after the chemical reaction which produces new products.

Hence all they involve chemical change.

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

pythagoras' theorem

square root (-5^2+9^2)

square root (25+81)

square root (106)

angle is tan^-1(9/5)

neg x, pos y