Admonishing Ray Elemental Spell

[Sing Sing]

Admonishing Ray:

You blast your enemies with rays of nonlethal force. You may fire one ray, plus one additional ray for every four levels you possess beyond 3rd (to a maximum of three rays at 11th level). Each ray requires a ranged touch attack to hit and deals 4d6 points of nonlethal damage. This is a force effect. The rays may be fired at the same or different targets, but all rays must be fired simultaneously and aimed at targets within 30 feet of each other.

The rays hit about as hard as a punch from a strong adult human, and can knock away unattended objects weighing up to 10 pounds if that amount of force could normally do so.
http://www.d20pfsrd.com/magic/all-spells/a/admonishing-ray

Can you damage undead with it as well in that way using elemental damage?

Elemental Spell:

Elemental Spell (Metamagic)
You can manipulate the elemental nature of your spells.

Benefit: Choose one energy type: acid, cold, electricity, or fire. You may replace a spell’s normal damage with that energy type or split the spell’s damage, so that half is of that energy type and half is of its normal type.

Level Increase: +1 (an elemental spell uses up a spell slot one level higher than the spell’s actual level.)

Special: You can gain this feat multiple times. Each time you must choose a different energy type.
http://www.d20pfsrd.com/feats/metamagic-feats/elemental-spell-metamagic