An student dropped their book from the top of a canyon into a river 40 meters below.

how long does it take for the book to hit the water?

2.0 s

2.9 s

4.3 s

Use this formula for an object starting from rest and accelerating:

Distance = (1/2) (acceleration) (time)²

In this problem, the distance is 40 meters, and acceleration is gravity.  

So . . .

40 m = (1/2) (9.8 m/s²) (time)²

Divide each side by  (4.9 m/s²) :

time² = (40 m) / (4.9 m/s²)

time² = 8.16 sec²

Take the square root of each side :

√(time²) = √(8.16 sec²)

time = 2.86 seconds

Round it to  2.9 sec (choice B)

they are non-matter

explanation:

they are non-matter. basically, any type of energy or any abstract concept is an example of something that does not matter. other examples include dreams, magnetism, radio, and hate

b.a device that inputs heat into a cool object