More help with physics! This time with cookies!

[Deathslayer7]

So this time, I'm still having trouble with rotational kinematics.

Problem:

A diver makes 2.5 complete revolutions on the way from a 10m platform to the water below. Assuming zerio intial velocity, calculate the average angular velocity for this dive.

My thoughts:

average angular velocity = delta theta/ delta time.

delta theta is given, time is the problem.

The velocity of the diver is freefall from graivty (although i cant remember the equation. If someone could post that, I would appreciate it.)

Using the freefall equation, you find the velocity as he hits the water. From there, you can find the time using

v=v(o)+a*t and theta= v(o)*t+.5a*t^2 by substituting in a.

Doing that, you solve for t, and find the time it took to hit the water.

From there, you substitute that back into the average equation to get your answer.

Are my thoughts correct? :smallconfused:

[Griever]

Probably going to get ninja'd a lot but, here we go some:

First, I would find the time it took him to hit the water, to find that you use this equation:

y(f) - y(i) = v(yi)t - .5gt^2

y(f) will be -10
y(i) will be 0
v(yi) will be 0
g = 9.8 (already have negative in problem)

So, when I put those in there, I'll get two times, disregard the negative one.

In 2.5 rotations, you have gone through 5pi radians, so, since average angular velocity is:

theta(f) - theta(i) / t(f) - t(i)

You plug in your time change, theta(i) is zero, theta(f) is 5pi, and you have your answer.

[Deathslayer7]

ah. i was wondering what acceleration is. And it's is gravity.

*smacks head*

Thank you.

Goes to do problem once more.

[Deathslayer7]

I got 3.499 rad/s, not including sig digits or anything.

Is that what you got?

and t= 1.429s

[Griever]

3.599 rad/s?

I got 10.995 rad/s, did you divide 5pi by the time 1.42857 sec?

[Deathslayer7]

no i only did 5/1.429.

*grumbles about the stupid pi i always forget about.

yes. so 10.99. Thank you. :smallsmile:

*hands over a bag of cookies*