ANS(num_cmp($Vmax, relTol => 2, units=>"kN",));

kN is a unit of force, not mass.

If the student responds 2000 N, WebWork Agrees, as expected.

If the student responds 449.6 lbf, WebWork tells the units a wrong. Why? (See http://www.endmemo.com/sconvert/knlbf.php)

If the student responds 449.6 lb, WebWork agrees, which is wrong, because lb is a unit of mass. The unit of force is lbf.

Next I set up a test problem with

ANS(num_cmp($Vmax, relTol => 2, units=>"kg",));

kg is a unit of mass.

If the student responds 4.4 lb, WebWork tells the units a wrong. Why?

If the student responds 4.4 lbf, gracefully, WebWork tells the units a wrong.

May be I am missing something? ...