Equation given -- s=6.1t^2, t is seconds.

Object dropped from 75 feet. Find the speed of the object at t = 3.

one question- is the 75 feet important? Or do you just plug in the 3 for t to get 54.9 ft/sec?

Any help is appreciated!

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- Jun 9th 2009, 05:41 PMlive_laugh_luv27Free fall
Equation given -- s=6.1t^2, t is seconds.

Object dropped from 75 feet. Find the speed of the object at t = 3.

one question- is the 75 feet important? Or do you just plug in the 3 for t to get 54.9 ft/sec?

Any help is appreciated! - Jun 9th 2009, 06:12 PMsa-ri-ga-ma
In the problem speed of the object is required.

Speed v = ds/dt.

In the problem 75 feet is necessary. Otherwise the object may reach the ground before 3 seconds. - Jun 9th 2009, 06:48 PMlive_laugh_luv27
ok..then how would I set this problem up?

- Jun 9th 2009, 09:51 PMyeongil
They are a lot of things wrong with the original post. First, let's look at the vertical motion equations on Earth:

= time (I'll assume it's in seconds)

= initial height

= initial velocity

= height after t sec

= velocity after t sec

The equation you've given us is

Does up => positive and down => negative? Or the other way around? If it is the former, then this equation is for an object that floats upwards. (In other words, is there a negative sign missing?)

Since the object is being dropped, the initial velocity is zero, so it's okay that there is no t term in the equation you gave us. But there is mention of the initial height at all. So the question is, is this the equation you meant to give us?

Quote:

Or do you just plug in the 3 for t to get 54.9 ft/sec?

**feet**, NOT a velocity of 54.9 ft/sec.

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