. Iron at 30 °C is put into thermal contact with an unknown material at 60 °C of equal mass. The equilibrium temperature is measured to be 50 °C. Which of the materials below could be the identity of the unknown material?

explanation:

as the height from which the ruler was dropped increased, the speed of the ruler at ryan's hand increased.

that tool is called an altimeter which measures your altitude which can be used to tell which atmosphere you are currently in, including the stratosphere.

hope this ! : )

the total distance that martina travels that day is

(distance from home to mom's office) plus (distance from mom's office to school)

plus (distance from school to library) plus (distance from library to friend's house)

plus (distance from friend's house to martina's house).

(we don't know what any of these distance actually is.)

3. dark matter

empty space could also be a simple vacuum