- #1

- 2

- 0

## Homework Statement

This isn't so much of a problem as a general question. I am trying to find the starting velocity of a spinning ball going upwards (in air, close to earth's surface, only force acting on it is the gravitational force) until its linear velocity reaches zero. I found the initial velocity two different ways (with mechanical energy and with kinematics), and I am getting answers that differ by a constant.

## Homework Equations

[itex]mgh=\frac{7}{10}mv_0^2[/itex]

[itex]v_f^2=v_0^2-2gh[/itex]

(where the final velocity is 0)

## The Attempt at a Solution

When I try to find the initial velocity, I can see that the two differ by a constant. I know that if the ball had no rotational kinetic energy, the equations would line up. However, I thought that the rotational motion would not have an effect on the linear motion of its center of mass. I think that the discrepancy is because the kinematics equation is derived from the conservation of energy of an object that has no rotational motion, but I'm not sure. I appreciate your help!