Work done by the hammer in a single stroke?

[fro]

Need some verification.

I am trying to drive a 9 inch nail into a log with a 10kg hammer, raising it to a maximum height of 1m and then gain momentum as it is swung down.

a. Energy of the hammer immediately prior to striking the nail:
$$10kg\times10\frac{m}{s^2}\times1m = 100J.$$

b. If 20% of hammer's energy is dissipated during the collision, how much energy is delivered to the nail in a single stroke provided the hammer remains at rest after hitting the nail?

$$80\%\times100J = 80J.$$

c. Work done by the hammer in a single stroke?

Shouldn't this be the 100J also?

d. How far into the log is the nail driven in a single stroke?

Not sure about this one!

Could someone please give me some hints on these. Thanks.

 

[OlderDan]

Did you state all the information you were given for this problem? It seems that some assumption is being made that I am not seeing, and since nobody else has replied I assume others are not seeing it either.