# Average acceleration and average force

## Homework Statement

Steel ball with a mass 17 grams, is launched at a speed of 6 m/s, into someones eye. The ball comes to a rest over a distance of 1mm.

A) What is the average acceleration experienced by the ball to stop it?

B) What is the deaccelerating force that must be exerted on the ball (by the eyeball), and thus, what is the average force on the eyeball?

## The Attempt at a Solution

I tried using the Vf^2 - Vi^2 = 2a*d (where d is displacement, vf is final veloctiy, vi is initial velocity and a is acceleration) but came out with -18m/s^2 for the acceleration. I dont think that is right however

Any help is greatly appreciated

## Answers and Replies

Doc Al
Mentor
Check your arithmetic.

I stuffed up the arithmetic.
Answer should be -1800. Is that right? Seems big for acceleration.

Check the numbers, I get an even bigger acceleration. Anyway yes, it is big for an acceleration, but also from 6 m/s (21.6 Km/h) to rest in only 1 mm is really a lot... to stop something that fast in such short distance will require (of course depending on mass) a huge force, at least for usual objects (therefore not too light).

Doc Al
Mentor
I stuffed up the arithmetic.
Answer should be -1800. Is that right? Seems big for acceleration.
You're still off by a factor of 10, so recheck that math. Yes, it's big. But 1 mm is a small distance to come to rest in.