Question

The collision between a hammer and a nail can be considered to be approximately elastic. Estimate the kinetic energy acquired by a 13 g nail when it is struck by a 550 g hammer moving with an initial speed of 4.1 m/s.

I am completely confused by this problem all of my answers have been off by orders of magnitude. My closest response was .23.

Answer 1

Energy in the hammer= energy in the nail

1/2 .550*4.1^2= KE

Answer 2

I got KE = 4.622 J and it isn't correct

Answer 3

I am troubled by the word "estimate" in the problem, and am uncertain what they are assuming about the hammer after impact.

Answer 4

If you approximate the hammer as being infinitely more massive than the nail, you can reason as follows.

In the rest frame of the hammer, the nail is intitially moving toward the hammer with e velocity of 4.1 m/s. After the collision it will move with the same velocity in the opposite direction. This means that in the original reference frame, the nail will have a velocity of 8.2 m/s.