Math CentralQuandaries & Queries


Subject: Motion problems: Freefalling objects
Name: Patricia
Who are you: Student

Hello! I am having difficulties involving this problem. can you help me? I have a test tomorrow about this. Can you answer me as soon as possible? Thanks!

How long will it take a stone dropped from atop a 1000-meter tall building to reach the ground?

Thanks, Patricia.

Hi Patricia.

The general equation of motion for an object under constant acceleration (like that due to gravity in your question) is this:

d=v0 t+½at2

where d is the displacement (distance), v0 is the initial velocity, a is the constant acceleration and t is the time.

In your case, you know d is 1000 m, v0 is 0 (it is dropped, not thrown), a is the standard for earth's gravity (9.8 m/s2 ) and you want to find t, which will be the time in seconds .

Substitute these into the equation and solve for t.

Hope this helps,
Stephen La Rocque.

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