# Help my girlfriend with average force, she has a test tomorrow! (Should be easy)

1. Feb 5, 2004

### Unknown

As a physics major, I feel kind of stupid asking this question, but my girlfriend was assigned a problem I just can't figure out. Hey, it's late.

A man throws a 7kg shot put with an initial speed of 13m/s. It goes 2.8m. What is the average force exerted?

2. Feb 6, 2004

### HallsofIvy

"average force"? Do you mean exerted by the thrower? You know that the person has accelerated the shot from 0 to 13 m/s but you don't know the time so you cannot calculate the (average) acceleration and so cannot calculate the (average) force applied. One could, theoretically, accelerate a mass over a very long time using a very low constant force or very quickly to the same speed using a very large constant force. In those two instances the "average" forces would be very different.

After he released the shot, the "average" force on the shot is, of course, the weight of the shot.

3. Feb 6, 2004

### Unknown

Thank you. I knew I didn't suck that much in my own major. That was what I told her I thought was the case, but I figured if it was in her book, it had to be right. My guess is she forgot to give me all of the problem.