# Pool ball question

1. Jun 24, 2012

### alanm

Hi All,

a cue stick strikes a stationary pool ball with an average force of 51N over a time of 12ms. the ball has a mass of 0.22kg, what speed does the ball have just after impact/

I am struggling with this.

thanks

2. Jun 24, 2012

### Staff: Mentor

If this is a homework question, this post should go over in the homework section. But with that said...

The force and the mass are sufficient to calculate the acceleration of the ball as the cue stick applies force to it. You know how long the acceleration lasts, and that will allow you to calculate the speed at the end of the acceleration.

(Note that this answer assumes that by "just after impact" you mean just after the impact is finished, at the end of the 12 ms period. If you mean just after the start of the impact when the cue stick first touches the ball at the beginning of the 12 ms period, then the answer is "zero because the ball is still stationary", just about to start moving. Only an evil professor with a wicked sense of humor would pose such a deceptive trick question... but such do exist).

3. Jun 24, 2012

### rcgldr

You're probably supposed to use the fact that change in momentum = force x time (impulse).

4. Jun 24, 2012

### Danger

Wow! I played in the world finals in Las Vegas 5 years in a row, and I have no idea as to your problem. It's just something that you feel.

5. Jun 25, 2012

### CWatters

Newton and the equations of motion..

f=ma
v=u+at

substitute.