Turntable Acceleration question

1. Sep 17, 2008

Husker70

1. The problem statement, all variables and given/known data
A point on a rotating turntable 20.0 cm from the center accelerates from rest to a final
speed of .700m/s in 1.75s. At t=1.25s, find the magnitude and direction of (a) the radial
acceleration, (b) the tangential acceleration, and (c) the total acceleration at that point

2. Relevant equations

3. The attempt at a solution
I get the speed by comparing the the speed at 1.75s to speed at 1.25. I get
this to be .5m/s
To find the radial acceleration at that point I do (.5m/s)2/.20m = 1.25m/s2
Is the tangential acceleration at that point 1.25/1.25? Which is the radial/time?
Kevin

2. Sep 17, 2008

LowlyPion

The tangential acceleration at that point is the change in tangential velocity. That would be the same acceleration you used to determine that it was moving at .5m/s namely (.7m/s) /1.75s

Presumably you know to sum the accelerations as vectors for the final answer..

3. Sep 17, 2008

Husker70

Thanks but that what I'm unsure of. I simply assumed that this is a constant acceleration
and so by simple comparing taking 1.75/.7=1.25/x, I get .5 m/s
Did I start that wrong?

Kevin

4. Sep 17, 2008

LowlyPion

You should expect that the acceleration is uniform, and that looked fine.

They should have said if it were not.

Good Luck.

5. Sep 17, 2008

Husker70

Is that tang acceleration correct by using the radial acceleration at that point/time?
So that 1.25m/s2/ 1.25s = 1 m/s2 for tang?

Thanks,
Kevin

6. Sep 17, 2008

LowlyPion

Oops the acceleration is inverted. It's .7/1.75. Sorry for swapping the two.

Last edited: Sep 17, 2008
7. Sep 17, 2008

LowlyPion

That means you have a forward acceleration of .7/1.75 = .4m/s2

The angle then is tan-1(.4/1.25) = 17.74 degrees (ratio of Opposite/adjacent with respect to forward of the radius.)

The magnitude is the RSS of .4 and 1.25 .

8. Sep 17, 2008

Husker70

Thanks,
That makes sense to me. Thanks for your time. I'm getting
ready to go take my first exam.

Take care,
Kevin

9. Sep 17, 2008

LowlyPion

Best of luck then.