limexx_35 Posts: 1, Reputation: 1 New Member #1 Oct 16, 2005, 03:01 PM
Can anyone help me with this problem?( science
A brick falls from the top of a building and strikes the ground with a velocity of 19.6m/s. How long does the brick fall?
 SSchultz0956 Posts: 121, Reputation: 10 Junior Member #2 Oct 17, 2005, 09:23 AM
Are you asking how long as in time or how long as in distance? Since Velosity = displacement/time elapsed does the problem give more information than the velocity? If so you could say time = V/displacement and Displacement = V* time
 Borewyrm Posts: 65, Reputation: 2 Junior Member #3 Jan 23, 2006, 07:52 PM
... acceleration due to gravity 9.81 meters per second squared... Its been ten years since high school but that is it no?
 dmatos Posts: 204, Reputation: 26 Full Member #4 Jan 23, 2006, 08:16 PM
Based on the number given in the question, I'd assume acceleration due to gravity is 9.8m/s^2.

The equation for velocity in terms of constant acceleration is:

v(t) = v0 + a*t

Where v0 is the initial velocity, a is the acceleration, and t is the time. You can now solve for time given v(t) = 19.6, v0 = 0, and a = 9.8.

If the question is asking "how long" in terms of total distance fallen (which I don't think it is), start by solving for the time, then use the formula

d = v0*t + a*t^2/2, which you get by integrating v(t) = v0 + a*t.
 rudi_in Posts: 251, Reputation: 45 Full Member #5 Jan 24, 2006, 07:15 PM
Thank you for posting your question to the Ask Me Help Desk!

I would go about solving this problem in the following manner...

acceleration = (final velocity - initial velocity) / time

Our acceleration in this problem is the acceleration due to gravity which is 9.8 m/s/s

Our final velocity is 19.6 m/s/s as indicated by the problem.

Our initial velocity is 0 m/s/s which is derived from the fact that before it began to fall off the building, it was not moving.

We can then solve for time.

9.8 = (19.6 - 0) / t

9.8 = 19.6/t

multiply both sides by t

9.8t = 19.6

divide both sides by 9.8

t = 2

The brick fell for 2 seconds.

I hope that this was helpful.

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