# Answer on Mechanics | Relativity Question for Jonathan

Question #14299

a worker drops a wrench from the top of a tower 80 meters tall. What is the velocity when the wrench strikes the ground assuming the acceleration to be -9.81 m/s^2

Expert's answer

At first, let's find the time needed to fall down from the height of 80 meters

from the equation

for displacement (assume the axis is directed downwards and

the origin is on the top of a tower):

h = g * t^2 / 2,

t = sqrt(2h /

g).

Now let's use the equation for the speed when the wrench falls

down:

V = g * t = g * sqrt(2h / g) = sqrt(2 * g * h).

So,

V =

sqrt(2 * 9.81 * 80) = 39.6 m/s.

from the equation

for displacement (assume the axis is directed downwards and

the origin is on the top of a tower):

h = g * t^2 / 2,

t = sqrt(2h /

g).

Now let's use the equation for the speed when the wrench falls

down:

V = g * t = g * sqrt(2h / g) = sqrt(2 * g * h).

So,

V =

sqrt(2 * 9.81 * 80) = 39.6 m/s.

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