Calculating Final velocity.

I've got to calculate the acceleration of an object falling freely by using the equation: (V^2-U^2)/t = a.
But, I don't have the final velocity. I know the initial velocity is 0. I also know that I can work out the average velocity using S = D/t. But, the average velocity doesn't give me the final velocity.
How would I find out purely the final velocity? This is using an experiment with 2 light gates, a tube and a wooden cork. The light gates are used to time how long the cork takes to fall through a clear tube of 1m.

Reply 1

troubadour.

Original post by Toffo132

Can you post a picture of the question? It would be easier to answer if you could. Thanks. :smile:

Reply 2

Toffo132

Original post by Hydeman

Can you post a picture of the question? It would be easier to answer if you could. Thanks. :smile:

It's not really a question, it's an experiment I'm planning. But basically I wanna find out Vf, but I don't have the acceleration. The Vi is 0m/s, the time taken will be determined when doing the experiment, and the distance will be 1m.

The aim is to find out the acceleration due to gravity (g) using suvat. I can draw a rough sketch of the experiment: http://i.imgur.com/QxKb3y7.png

I'm confused as to whether I use the average velocity, or the FINAL velocity (and if so how to get it)

Edit: Also, what on earth would be the independent variable to this? I'm not changing anything. Derp.

(edited 8 years ago)

Reply 3

troubadour.

Original post by Toffo132

Wouldn't the acceleration be g? I mean, if you want to work out g using SUVAT, then you'll need some way to measure the final velocity so that the only term that's left in the equation that you don't know is acceleration (which would be g on Earth). There's really no way that I can think of of calculating the final velocity using SUVAT without using g...

Haha, for independent variable you could use height or the mass of the object being dropped? That's what Galileo did. :tongue:

Reply 4

Toffo132

Original post by Hydeman

This is where i'm confused. Would using the average velocity from the top of the tube to the bottom work? It's the only way I can think of getting this to work.

Reply 5

troubadour.

Original post by Toffo132

This is where i'm confused. Would using the average velocity from the top of the tube to the bottom work? It's the only way I can think of getting this to work.

You could use that but it would probably give you an inaccurate answer unless the drop is almost instantaneous (<1 second), in which case you could make the crude assumption that the final velocity is more or less equal to the average velocity as the mass didn't have much time to accelerate before hitting the bottom of the tube.

Reply 6

Toffo132

Original post by Hydeman

To find the acceleration without the Vf, would s = ut + 0.5at^2 work?

Reply 7

troubadour.

Original post by Toffo132

To find the acceleration without the Vf, would s = ut + 0.5at^2 work?

Hmm, I don't see why not! xD This explains why I got a B in A-level mathematics: I look for complicated solutions to simple problems. :lol:

That equation should work because the acceleration is constant and unlike the other equation you mentioned in the OP, there is only one term that you don't know instead of two. :smile:

Reply 8

Toffo132

any idea how i'd rearrange that for a? :s-smilie:

Reply 9

Rump Steak

Original post by Toffo132

any idea how i'd rearrange that for a? :s-smilie:

You'd find it a lot easier to sub in all the values first, then rearrange at the end :smile:

Reply 10

troubadour.

Original post by Toffo132

any idea how i'd rearrange that for a? :s-smilie:

Original post by Rump Steak

You'd find it a lot easier to sub in all the values first, then rearrange at the end :smile:

As Rump Steak said, it's probably easier to rearrange when you have numbers than trying to do it algebraically. But here's my rearrangement anyway: a = [2(s - ut)]/t². It's a mess, really. Which is why you should do it Rump Steak's way. :biggrin: