A squirrel drops an acorn onto the head of an unsuspecting dog. The acorn falls 4.0\,\text m4.0m4, point, 0, start text, m, end text before it lands on the dog. We can ignore air resistance. How many seconds did the acorn fall?

0.903 seconds

Explanation:

To find how many seconds the acorn fall, we can use the formula for distance travelled with constant acceleration:

D = Vo*t + a*t^2/2,

where D is the distance travelled, Vo is the inicial speed, t is the time and a is the acceleration.

In our problem:

Vo = 0,

a = g = 9.81 m/s2,

D = 4 meters.

So, we can solve the equation to find the time:

4 = 0*t +9.81*t^2/2

4.905*t^2 = 4

t^2 = 4/4.905 = 0.8155

t =   0.903 seconds