Agirl on a bridge throws a rock
straight down at -12.5 m/s. it hits
the ground 38.4 m below.
how much time did it take?
(unit = s)

The amount of time it will take to reach the ground is 1.3 secs

To get the time it will take, we will use the equation of motion expressed as:

v is the final velocity

u is the initial velocity

g is the acceleration due to gravity

t is the time taken

Given the following parameters

v = 0m/s

u = -12.5m/s

g = 9.8m/s²

Substitute the given parameters into the formula to get the time taken as shown:

Hence the amount of time it will take to reach the ground is 1.3 secs

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t = 1.3 s.

To solve this exercise we have to use the freefall equation t = (v-v₀)/g. v = 0 due the final velocity when the rock reach the ground is 0.

With v₀ = -12.5m/s and g = 9.8m/s²

t = -(-12.5m/s)/9.8m/s²

t = 1.3 s

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