# Force of nail after being struck by a hammer

## Homework Statement

A 5lb hammerhead, traveling at 5.4ft/s strikes a nail and is brought to a stop in .00081s. The acceleration of gravity is 32ft/s^2, What force did the nail recieve?

## Homework Equations

The equation I have is F=Pf-Pi/delta T. Both Pf and Pi have a arrow above them going to the right.

## The Attempt at a Solution

I know I have to find Pf and Pi, and P=mv. With that said would Pf be 0, since it comes to a stop, and Pi be (5lb)(5.4ft/s)? And I am guessing that delta T would .00081s?

LowlyPion
Homework Helper

## Homework Statement

A 5lb hammerhead, traveling at 5.4ft/s strikes a nail and is brought to a stop in .00081s. The acceleration of gravity is 32ft/s^2, What force did the nail recieve?

## Homework Equations

The equation I have is F=Pf-Pi/delta T. Both Pf and Pi have a arrow above them going to the right.

## The Attempt at a Solution

I know I have to find Pf and Pi, and P=mv. With that said would Pf be 0, since it comes to a stop, and Pi be (5lb)(5.4ft/s)? And I am guessing that delta T would .00081s?

Welcome to PF.

The real question here is what is the mass of the hammerhead? Since they give you acceleration of 32ft/s2, then this suggests to me this is how much it weighs. So I would say you need to determine your mass as 5/32 and then multiply by your 5.4 to get your momentum and then proceed as you were apparently intending.

Welcome to PF.

The real question here is what is the mass of the hammerhead? Since they give you acceleration of 32ft/s2, then this suggests to me this is how much it weighs. So I would say you need to determine your mass as 5/32 and then multiply by your 5.4 to get your momentum and then proceed as you were apparently intending.

So, p=mv which would be p=(5/32)(5.4) which equals .84375.
Then, F=Pf-Pi/delta T, which would be (0)-(.84375)/(.00081)-(0), which would equal -1041.67 N, but you cant have a negative force can you? Am I doing this right, or am I missing something?

LowlyPion
Homework Helper
So, p=mv which would be p=(5/32)(5.4) which equals .84375.
Then, F=Pf-Pi/delta T, which would be (0)-(.84375)/(.00081)-(0), which would equal -1041.67 N, but you cant have a negative force can you? Am I doing this right, or am I missing something?

Which direction did you choose as + ?
And what is the question asking?
What force did the nail recieve?
So if the impact of the hammer resulted in a (-) force to the hammer that sounds like it received an upward force and the nail received a downward force.