Homework Help: Rotational Motion of a baseball

1. Feb 21, 2016

manuel60

1. The problem statement, all variables and given/known data
A major-League pitcher throws a baseball towards home plate. the ball rotates at 1560 rpms,and it travels 18.5 meters to the plate at an average translational speed of 40.2m/s.how many revolutions does the ball make during this trip?

2. Relevant equations

3. The attempt at a solution
(2)(pi)(1560)/60=163.362818

2. Feb 21, 2016

SteamKing

Staff Emeritus
What's the 2π for?

The question asks how many revolutions the ball makes during its trip to home plate. You didn't even calculate how long it takes the ball to make this trip.

3. Feb 21, 2016

manuel60

I have trouble with rotational motion so I am honestly not sure what I am doing?
sorry I have a horrible teacher all she does is give us work and notes and doesn't actually teach

4. Feb 21, 2016

SteamKing

Staff Emeritus
Terrible, but irrelevant.

If an object rotates at 10 revolutions per minute (RPM), how many revolutions does it make in one minute? In ten minutes?

You don't need a world-class physicist to teach you this.

5. Feb 21, 2016

Cozma Alex

Because of the momentum conservation (during the motion only the weight acts on the ball but it's torque is 0) the ball maintain its frequency of rotation during it's journey, the frequency is given by the number of revolutions n divided by time, you have to get n
Since you have f the only thing you need to get n is the time of the journey, this is a parabolic motion, you have info on the horizontal axis

Last edited: Feb 21, 2016